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Astrophysics and Star Formation Studies

Works Count: 82226

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This cluster of papers covers a wide range of topics related to star formation, including the formation of stars in molecular clouds, the evolution of protoplanetary disks, the role of interstellar dust and turbulence, astrochemistry, and the influence of magnetic fields on the process. It also explores the characteristics of young stellar objects and accretion disks in various stages of star formation.

Keywords

Star Formation; Molecular Clouds; Protoplanetary Disks; Interstellar Dust; Turbulence; Astrochemistry; Young Stellar Objects; Accretion Disks; Interstellar Medium; Magnetic Fields

The star formation law in galactic disks

1989-09-01

Jr. Kennicutt Robert C.

view Abstract Citations (1672) References (105) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Star Formation Law in Galactic Disks Kennicutt, Robert C., Jr. Abstract Measurements of … view Abstract Citations (1672) References (105) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Star Formation Law in Galactic Disks Kennicutt, Robert C., Jr. Abstract Measurements of the distribution of Hα emission in galaxies have been combined with published H I and CO data, in order to reassess the dependence of the massive star formation rate (SFR) on the density and dynamics of the interstellar gas. The disk-averaged Hα surface brightness is correlated with the mean atomic and total gas surface densities, but is only weakly correlated with the mean molecular gas density inferred from CO emission. Radial profiles of gas and Hα emission in 15 galaxies have been used to define the relationship between the SFR and gas surface density. In dense regions the SFR and total gas density are well represented by a Schmidt power-law relation (R = a{SIGMA}^N^_g_), with index N = 1.3 +/- 0.3, and nearly the same value for the zero point a, at least for the galaxies in our sample. This Schmidt law breaks down, however, at densities below a critical threshold value. Massive star formation is completely suppressed at surface densities well below the threshold, while at densities near the the threshold value the slope of the SFR-density relation is much steeper than a normal Schmidt law. The observed threshold densities vary by an order of magnitude among the galaxies in our sample and appear to be largely independent of whether the predominant gas phase is atomic or molecular. The star formation threshold appears to be associated with the onset of large-scale gravitational instabilities in the gas disks. A simple single-fluid (Toomre) disk stability model predicts threshold densities and radii which are in excellent agreement with the observations. The same analysis demonstrates that the radial distribution of gas in late-type galaxies closely follows the threshold surface density, confirming a hypothesis originally proposed by Quirk, and indicating the importance of star formation thresholds in virtually all parts of the disk. The combination of a nearly linear star formation law at high densities with a strongly nonlinear SFR-density law near the threshold redresses many of the previous observational difficulties with the Schmidt law and may provide physical insights into such diverse phenomena as nuclear and disk starbursts, the suppression of star formation in gas-rich S0 galaxies and low surface brightness galaxies, star formation in spiral arms, the observation of radial cutoffs to stellar disks, and the star formation histories of disk galaxies. Publication: The Astrophysical Journal Pub Date: September 1989 DOI: 10.1086/167834 Bibcode: 1989ApJ...344..685K Keywords: Galactic Evolution; H Alpha Line; H Ii Regions; Interstellar Gas; Star Formation Rate; Emission Spectra; Gas Dynamics; Radial Distribution; Spiral Galaxies; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: STELLAR CONTENT; STARS: FORMATION full text sources ADS | data products NED (34) SIMBAD (33)

The size distribution of interstellar grains

1977-10-01

J. S. Mathis , William M. Rumpl , K. H. Nordsieck

view Abstract Citations (3560) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The size distribution of interstellar grains. Mathis, J. S. ; Rumpl, W. ; Nordsieck, … view Abstract Citations (3560) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The size distribution of interstellar grains. Mathis, J. S. ; Rumpl, W. ; Nordsieck, K. H. Abstract The observed interstellar extinction over the wavelength range 0.11 μm < λ < 1 μm was fitted with a very general particle size distribution of uncoated graphite, enstatite, olivine, silicon carbide, iron, and magnetite. Combinations of these materials, up to three at a time, were considered. The cosmic abundances ofthe various constituents were taken into account as constraints on the possible distributions of particle sizes. Excellent fits to the interstellar extinction, including the narrowness of the λ2160 feature, proved possible. Graphite was a necessary component of any good mixture, but it could be used with any of the other materials. The particle size distributions are roughly power law in nature, with an exponent of about -3.3 to -3.6. The size range for graphite is about 0.005 μm to about 1 μm. The size distribution for the other materials is also approximately power law in nature, with the same exponent, but there is a narrower range of sizes: about 0.025-0.25 μm, depending on the material. The number of large particles is not well determined, because they are gray. Similarly, the number of small particles is not well determined because they are in the Rayleigh limit. This power-law distribution is drastically different from an Oort-van de Hulst distribution, which is much more slowly varying for small particles but drops much faster for particles larger than average. The extinction was also fitted with spherical graphite particles plus cylinders of each of the other materials. Linear and circular polarizations were then determined for the cylinders on the assumption of Davis-Greenstein alignment. The extinction was quite satisfactory, but the linear polarization reached a maximum in the ultraviolet (about 1600 Å). This is because the mixture contains many small particles. Ifthe small particles are not elongated or aligned, the wavelength dependence of the polarization can be fitted, but the larger particles which are aligned do not provide enough polarization per magnitude of extinction. However, a fit to polarization and extinction can be achieved if the material responsible for the polarization contributes only a small part of the extinction but consists of fairly large particles and is very well aligned. Dielectric particles with coatings could also provide the polarization. Subject headings: interstellar : matter «— polarization — Publication: The Astrophysical Journal Pub Date: October 1977 DOI: 10.1086/155591 Bibcode: 1977ApJ...217..425M Keywords: Cosmic Dust; Interstellar Extinction; Interstellar Matter; Particle Size Distribution; Enstatite; Graphite; Magnetite; Olivine; Polarization Characteristics; Ultraviolet Astronomy; Astrophysics full text sources ADS | data products SIMBAD (1)

Orbital migration of the planetary companion of 51 Pegasi to its present location

1996-04-01

D. N. C. Lin , Peter Bodenheimer , D. C. Richardson

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Turbulence and star formation in molecular clouds

1981-04-01

Richard B. Larson

Data for many molecular clouds and condensations show that the internal velocity dispersion of each region is well correlated with its size and mass, and these correlations are approximately of … Data for many molecular clouds and condensations show that the internal velocity dispersion of each region is well correlated with its size and mass, and these correlations are approximately of power-law form. The dependence of velocity dispersion on region size is similar to the Kolmogoroff law for subsonic turbulence, suggesting that the observed motions are all part of a common hierarchy of interstellar turbulent motions. The regions studied are mostly gravitationally bound and in approximate virial equilibrium. However, they cannot have formed by simple gravitational collapse, and it appears likely that molecular clouds and their substructures have been created at least partly by processes of supersonic hydrodynamics. The hierarchy of subcondensations may terminate with objects so small that their internal motions are no longer supersonic; this predicts a minimum protostellar mass of the order of a few tenths of a solar mass. Massive 'protostellar' clumps always have supersonic internal motions and will therefore develop complex internal structures, probably leading to the formation of many pre-stellar condensation nuclei that grow by accretion to produce the final stellar mass spectrum. Molecular clouds must be transient structures, and are probably dispersed after not much more than 107 yr.

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The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems

2002-01-04

Pavel Kroupa

The distribution of stellar masses that form in one star formation event in a given volume of space is called the initial mass function (IMF). The IMF has been estimated … The distribution of stellar masses that form in one star formation event in a given volume of space is called the initial mass function (IMF). The IMF has been estimated from low-mass brown dwarfs to very massive stars. Combining IMF estimates for different populations in which the stars can be observed individually unveils an extraordinary uniformity of the IMF. This general insight appears to hold for populations including present-day star formation in small molecular clouds, rich and dense massive star-clusters forming in giant clouds, through to ancient and metal-poor exotic stellar populations that may be dominated by dark matter. This apparent universality of the IMF is a challenge for star formation theory, because elementary considerations suggest that the IMF ought to systematically vary with star-forming conditions.

Submillimeter continuum observations of Rho Ophiuchi A - The candidate protostar VLA 1623 and prestellar clumps

1993-03-01

P. André , D. Ward‐Thompson , M. Barsony

view Abstract Citations (1129) References (94) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Submillimeter Continuum Observations of rho Ophiuchi A: The Candidate Protostar VLA 1623 and Prestellar … view Abstract Citations (1129) References (94) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Submillimeter Continuum Observations of rho Ophiuchi A: The Candidate Protostar VLA 1623 and Prestellar Clumps Andre, Philippe ; Ward-Thompson, Derek ; Barsony, Mary Abstract Submillimeter continuum mapping of the Rho Ophiuchi A cloud core reveals four compact clumps with masses less than about 1 solar mass embedded in an arcshaped ridge of total mass about 15 solar, lying at the edge of the compact H II region around the B3 star S1. Three of the clumps appear amorphous in shape and are probably prestellar in nature. The fourth clump is the best defined and coldest and coincides with the young stellar object (YSO) VLA 1623. It is suggested that this object is a protostar whose circumstellar material is distributed in a 'cored-apple' envelope. The density gradient appears to be that of a centrally heated envelope or of an isothermal envelope with no central heating object. The mass ejection of VLA 1623 appears to be extremely efficient and implies that a global MHD approach to infall and outflow may be required to explain the youngest embedded sources. It is suggested that VLA 1623 and a few other low-luminosity YSOs make up an entirely new class of YSOs. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/172425 Bibcode: 1993ApJ...406..122A Keywords: Early Stars; Protostars; Star Formation; Stellar Structure; Cosmic Dust; Energy Distribution; Submillimeter Waves; Astrophysics; ISM: JETS AND OUTFLOWS; ISM: INDIVIDUAL ALPHANUMERIC: VLA 1623; STARS: INDIVIDUAL CONSTELLATION NAME: RHO OPHIUCHI A; STARS: PRE--MAIN-SEQUENCE; RADIO CONTINUUM: STARS full text sources ADS | data products SIMBAD (25)

GLIMPSE. I. AnSIRTFLegacy Project to Map the Inner Galaxy

2003-08-01

Robert A. Benjamin , E. Churchwell , B. Babler +7 more

The Galactic Legacy Infrared Mid‐Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion‐limited infrared survey of 2/3 of the inner … The Galactic Legacy Infrared Mid‐Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion‐limited infrared survey of 2/3 of the inner Galactic disk with a pixel resolution of ∼12 using the Infrared Array Camera at 3.6, 4.5, 5.8, and 8.0 μm. The survey will cover Galactic latitudes |b|≤1° and longitudes |l| = 10°–65° (both sides of the Galactic center). The survey area contains the outer ends of the Galactic bar, the Galactic molecular ring, and the inner spiral arms. The GLIMPSE team will process these data to produce a point‐source catalog, a point‐source data archive, and a set of mosaicked images. We summarize our observing strategy, give details of our data products, and summarize some of the principal science questions that will be addressed using GLIMPSE data. Up‐to‐date documentation, survey progress, and information on complementary data sets are available on the GLIMPSE Web site.

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Instability, turbulence, and enhanced transport in accretion disks

1998-01-01

Steven A. Balbus , John F. Hawley

Recent years have witnessed dramatic progress in our understanding of how turbulence arises and transports angular momentum in astrophysical accretion disks. The key conceptual point has its origins in work … Recent years have witnessed dramatic progress in our understanding of how turbulence arises and transports angular momentum in astrophysical accretion disks. The key conceptual point has its origins in work dating from the 1950s, but its implications have been fully understood only in the last several years: the combination of a subthermal magnetic field (any nonpathological configuration will do) and outwardly decreasing differential rotation rapidly generates magnetohydrodynamic (MHD) turbulence via a remarkably simple linear instability. The result is a greatly enhanced effective viscosity, the origin of which had been a long-standing problem. The MHD nature of disk turbulence has linked two broad domains of magnetized fluid research: accretion theory and dynamos. The understanding that weak magnetic fields are not merely passively acted upon by turbulence, but actively generate it, means that the assumptions of classical dynamo theory break down in disks. Paralleling the new conceptual understanding has been the development of powerful numerical MHD codes. These have taught us that disks truly are turbulent, transporting angular momentum at greatly enhanced rates. We have also learned, however, that not all forms of disk turbulence do this. Purely hydrodynamic turbulence, when it is imposed, simply causes fluctuations without a significant increase in transport. The interplay between numerical simulation and analytic arguments has been particularly fruitful in accretion disk theory and is a major focus of this article. The authors conclude with a summary of what is now known of disk turbulence and mention some knotty outstanding questions (e.g., what is the physics behind nonlinear field saturation?) for which we may soon begin to develop answers.

Local Three-dimensional Magnetohydrodynamic Simulations of Accretion Disks

1995-02-01

John F. Hawley , Charles F. Gammie , Steven A. Balbus

view Abstract Citations (1024) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Local Three-dimensional Magnetohydrodynamic Simulations of Accretion Disks Hawley, John F. ; Gammie, Charles F. … view Abstract Citations (1024) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Local Three-dimensional Magnetohydrodynamic Simulations of Accretion Disks Hawley, John F. ; Gammie, Charles F. ; Balbus, Steven A. Abstract We have performed three-dimensional magnetohydrodynamic numerical simulations of an accretion disk to study the nonlinear development of the magnetorotational instability. We use a disk model that is local in the sense that it incorporates tidal and Coriolis forces but neglects background gradients in pressure and density. For simplicity we omit the vertical component of gravity and employ periodic boundary conditions in the vertical and azimuthal directions, and shearing-periodic boundary conditions in the radial direction. Our numerical method is an implementation of the "method of characteristics-constrained transport" algorithm. Most of the simulations begin with either a purely vertical or purely azimuthal magnetic field. Our major result is that turbulence is initiated and sustained by the magnetic instability. We provide a detailed characterization of the saturated turbulent state. The turbulence is anisotropic in a sense that implies an outward flux of angular momentum. The turbulent energy and angular momentum flux is dominated by magnetic stress rather than Reynolds stress. Most of the energy and angular momentum flux is concentrated at the largest scales. We find that the magnetic energy density in the saturated state is proportional to the product of the size of the simulation box and the initial field strength and is independent of the sound speed. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175311 Bibcode: 1995ApJ...440..742H Keywords: ACCRETION; ACCRETION DISKS; INSTABILITIES; MAGNETOHYDRODYNAMICS: MHD full text sources ADS |

Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - Auto exhaust along the Milky Way

1985-03-01

L. J. Allamandola , A. G. G. M. Tielens , John R. Barker

Search Bar to Enter New Query quick field: Author First Author Abstract Year Fulltext Select a field or operator abstract abstract only acknowledgements affiliation arXiv category author count author bibcode … Search Bar to Enter New Query quick field: Author First Author Abstract Year Fulltext Select a field or operator abstract abstract only acknowledgements affiliation arXiv category author count author bibcode bibliographic group bib abbrev, e.g. ApJ body of article data archive collection citation count doctype doi entdate first author fulltext identifier inst keyword object orcid page property publication full name date published title volume year citations() pos() references() reviews() similar() topn() trending() useful() single wildcard: ? wildcard: * exact match: = All Search Terms Your search returned 0 results Your search returned 0 results

A survey for circumstellar disks around young stellar objects

1990-03-01

Steven V. W. Beckwith , Anneila I. Sargent , R. Chini +1 more

Continuum observations at 1.3 mm of 86 pre-main sequence stars in the Taurus-Auriga dark clouds show that 42% have detectable emission from small particles. The detected fraction is only slightly … Continuum observations at 1.3 mm of 86 pre-main sequence stars in the Taurus-Auriga dark clouds show that 42% have detectable emission from small particles. The detected fraction is only slightly smaller for the weak-line and "naked" T Tauri stars than for classical T Tauris, indicating that the former stars often have circumstellar material. In both categories, the column densities of particles are too large to be compatible with spherical distributions of circumstellar matter -- the optical extinctions would be too large; the particles are almost certainly in spatially thin, circumstellar disks. Models of the spectral energy distributions from 10 to 1300 μm indicate that for the most part the disks are transparent at 1.3 mm, although the innermost (≪1 AU) regions are opaque even at millimeter wavelenths. The aggregate particle masses are between 10-5 and 10-2 M⊙. The disk mass does not decrease with increasing stellar age up to at least 107 years among the stars detected at 1.3 mm. There is some evidence for temperature evolution, in the sense that older disks are colder and less luminous. There is little correlation between disk mass and Hα equivalent width among the detected stars, suggesting that the Hα line is not by itself indicative of disk mass. Spectral indices for several sources between 1.3 and 2.7 mm suggest that the particle emissivities ɛ are weaker functions of frequency ν than is the usual case of interstellar grains. Particle growth via adhesion in the dense disks might explain this result. The typical disk has an angular momentum comparable to that generally accepted for the early solar nebula, but very little stored energy, almost five orders of magnitude smaller than that of the central star. Our results demonstrate that disks more massive than the minimum mass of the proto-solar system commonly accompany the birth of solar-mass stars and suggest that planetary systems are common in the Galaxy.

Dust Grain–Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud

2001-02-10

Joseph C. Weingartner , B. T. Draine

We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient very small carbonaceous grains (including … We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient very small carbonaceous grains (including polycyclic aromatic hydrocarbon molecules) to account for the observed infrared and microwave emission from the diffuse interstellar medium. Our distributions reproduce the observed extinction of starlight, which varies depending upon the interstellar environment through which the light travels. As shown by Cardelli, Clayton & Mathis in 1989, these variations can be roughly parameterized by the ratio of visual extinction to reddening, R_V. We adopt a fairly simple functional form for the size distribution, characterized by several parameters. We tabulate these parameters for various combinations of values for R_V and b_C, the C abundance in very small grains. We also find size distributions for the line of sight to HD 210121, and for sightlines in the LMC and SMC. For several size distributions, we evaluate the albedo and scattering asymmetry parameter, and present model extinction curves extending beyond the Lyman limit.

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Interstellar polycyclic aromatic hydrocarbons - The infrared emission bands, the excitation/emission mechanism, and the astrophysical implications

1989-12-01

L. J. Allamandola , G. G. M. Tielens , John R. Barker

view Abstract Citations (1177) References (151) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Polycyclic Aromatic Hydrocarbons: The Infrared Emission Bands, the Excitation/Emission Mechanism, and the Astrophysical … view Abstract Citations (1177) References (151) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interstellar Polycyclic Aromatic Hydrocarbons: The Infrared Emission Bands, the Excitation/Emission Mechanism, and the Astrophysical Implications Allamandola, L. J. ; Tielens, A. G. G. M. ; Barker, J. R. Abstract A comprehensive study of the PAH hypothesis is presented, including the interstellar, IR spectral features which have been attributed to emission from highly vibrationally excited PAHs. Spectroscopic and IR emission features are discussed in detail. A method for calculating the IR fluorescence spectrum from a vibrationally excited molecule is described. Analysis of interstellar spectrum suggests that the PAHs which dominate the IR spectra contain between 20 and 40 C atoms. The results are compared with results from a thermal approximation. It is found that, for high levels of vibrational excitation and emission from low-frequency modes, the two methods produce similar results. Also, consideration is given to the relationship between PAH molecules and amorphous C particles, the most likely interstellar PAH molecular structures, the spectroscopic structure produced by PAHs and PAH-related materials in the UV portion of the interstellar extinction curve, and the influence of PAH charge on the UV, visible, and IR regions. Publication: The Astrophysical Journal Supplement Series Pub Date: December 1989 DOI: 10.1086/191396 Bibcode: 1989ApJS...71..733A Keywords: Aromatic Compounds; Cyclic Hydrocarbons; Emission Spectra; Infrared Radiation; Interstellar Matter; Astronomical Spectroscopy; Deuterium; Interstellar Chemistry; Interstellar Extinction; Molecular Excitation; Astrophysics; INTERSTELLAR: GRAINS; MOLECULAR PROCESSES full text sources ADS | data products SIMBAD (7)

On the Density of Neutral Hydrogen in Intergalactic Space.

1965-11-01

James E. Gunn , B. A. Peterson

Density of neutral hydrogen in intergalactic space, using spectroscopic examination of quasi- stellar source 3C 9 Density of neutral hydrogen in intergalactic space, using spectroscopic examination of quasi- stellar source 3C 9

The Formation of the First Star in the Universe

2002-01-04

Tom Abel , Greg L. Bryan , Michael L. Norman

We describe results from a fully self-consistent three-dimensional hydrodynamical simulation of the formation of one of the first stars in the Universe. In current models of structure formation, dark matter … We describe results from a fully self-consistent three-dimensional hydrodynamical simulation of the formation of one of the first stars in the Universe. In current models of structure formation, dark matter initially dominates, and pregalactic objects form because of gravitational instability from small initial density perturbations. As they assemble via hierarchical merging, primordial gas cools through ro-vibrational lines of hydrogen molecules and sinks to the center of the dark matter potential well. The high-redshift analog of a molecular cloud is formed. As the dense, central parts of the cold gas cloud become self-gravitating, a dense core of approximately 100 M (where M is the mass of the Sun) undergoes rapid contraction. At particle number densities greater than 10(9) per cubic centimeter, a 1 M protostellar core becomes fully molecular as a result of three-body H2 formation. Contrary to analytical expectations, this process does not lead to renewed fragmentation and only one star is formed. The calculation is stopped when optical depth effects become important, leaving the final mass of the fully formed star somewhat uncertain. At this stage the protostar is accreting material very rapidly (approximately 10(-2) M year-1). Radiative feedback from the star will not only halt its growth but also inhibit the formation of other stars in the same pregalactic object (at least until the first star ends its life, presumably as a supernova). We conclude that at most one massive (M 1 M) metal-free star forms per pregalactic halo, consistent with recent abundance measurements of metal-poor galactic halo stars.

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Infrared Emission from Interstellar Dust. IV. The Silicate‐Graphite‐PAH Model in the Post‐SpitzerEra

2007-03-06

B. T. Draine , Aigen Li

IR emission spectra are calculated for dust heated by starlight, for mixtures of amorphous silicate and graphitic grains, including varying amounts of PAH particles. The models are constrained to reproduce … IR emission spectra are calculated for dust heated by starlight, for mixtures of amorphous silicate and graphitic grains, including varying amounts of PAH particles. The models are constrained to reproduce the average Milky Way extinction curve. The calculations include the effects of single-photon heating. Updated IR absorption properties for the PAHs are presented that are consistent with observed emission spectra, including those newly obtained by Spitzer. We find a size distribution for the PAHs giving emission band ratios consistent with the observed spectra of the Milky Way and other galaxies. Emission spectra are presented for a wide range of starlight intensities. We calculate how the efficiency of emission into different IR bands depends on PAH size; the strong 7.7 μm emission feature is produced mainly by PAH particles containing <103 C atoms. We also calculate how the emission spectrum depends on U, the starlight intensity relative to the local interstellar radiation field. The submillimeter and far-infrared emission is compared to the observed emission from the local interstellar medium. Using a simple distribution function, we calculate the emission spectrum for dust heated by a distribution of starlight intensities, such as occurs within galaxies. The models are parameterized by the PAH mass fraction qPAH, the lower cutoff Umin of the starlight intensity distribution, and the fraction γ of the dust heated by starlight with U > Umin. We present graphical procedures using Spitzer IRAC and MIPS photometry to estimate the parameters qPAH, Umin, and γ, the fraction fPDR of the dust luminosity coming from photodissociation regions with U > 100, and the total dust mass Mdust.

Control of star formation by supersonic turbulence

2004-01-07

Mordecai‐Mark Mac Low , Ralf S. Klessen

Understanding the formation of stars in galaxies is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay … Understanding the formation of stars in galaxies is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay between gravity and magnetostatic support, modulated by ambipolar diffusion. Recently, however, both observational and numerical work has begun to suggest that support by supersonic turbulence rather than magnetic fields controls star formation. In this review we outline a new theory of star formation relying on the control by turbulence. We demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. (ABSTRACT ABBREVIATED)

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Mass, luminosity, and line width relations of Galactic molecular clouds

1987-08-01

P. M. Solomon , A. R. Rivolo , John W. Barrett +1 more

view Abstract Citations (1511) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass, Luminosity, and Line Width Relations of Galactic Molecular Clouds Solomon, P. M. ; … view Abstract Citations (1511) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass, Luminosity, and Line Width Relations of Galactic Molecular Clouds Solomon, P. M. ; Rivolo, A. R. ; Barrett, J. ; Yahil, A. Abstract The authors present measurements of the velocity line width, size, virial mass, and CO luminosity for 273 molecular clouds in the Galactic disk between longitudes of 8° and 90°. These are obtained from three-dimensional data in the Massachusetts-Stony Brook CO Galactic Plane Survey. It is shown that the molecular clouds are in or near virial equilibrium and are not confined by pressure equilibrium with a warm or hot phase of interstellar matter. The velocity line width is proportional to the 0.5 power of the size, σv ∝ S0.5. A tight relationship, over four orders of magnitude, is found between the cloud dynamical mass, as measured by the virial theorem, and the CO luminosity M ∝ (LCO)0.81. The cloud CO luminosity is LCO∝ σv5. Publication: The Astrophysical Journal Pub Date: August 1987 DOI: 10.1086/165493 Bibcode: 1987ApJ...319..730S Keywords: Mass Distribution; Mass To Light Ratios; Milky Way Galaxy; Molecular Clouds; Spectral Line Width; Astronomical Catalogs; Astronomical Models; Astronomical Spectroscopy; Carbon Monoxide; Virial Theorem; Astrophysics; GALAXIES: THE GALAXY; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (272)

Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium

2001-06-20

Aigen Li , B. T. Draine

We present a quantitative model for the infrared emission from dust in the diffuse interstellar medium. The model consists of a mixture of amorphous silicate grains and carbonaceous grains, each … We present a quantitative model for the infrared emission from dust in the diffuse interstellar medium. The model consists of a mixture of amorphous silicate grains and carbonaceous grains, each with a wide size distribution ranging from molecules containing tens of atoms to large grains ≳1 μm in diameter. We assume that the carbonaceous grains have properties like polycyclic aromatic hydrocarbons (PAHs) at very small sizes and graphitic properties for radii a ≳ 50 Å. On the basis of recent laboratory studies and guided by astronomical observations, we propose "astronomical" absorption cross sections for use in modeling neutral and ionized PAHs from the far-ultraviolet to the far-infrared. We also propose modifications to the far-infrared emissivity of "astronomical silicate." We calculate energy distribution functions for small grains undergoing "temperature spikes" caused by stochastic absorption of starlight photons using realistic heat capacities and optical properties. Using a grain-size distribution consistent with the observed interstellar extinction, we are able to reproduce the near-IR to submillimeter emission spectrum of the diffuse interstellar medium, including the PAH emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm. The model is compared with the observed emission at high Galactic latitudes as well as in the Galactic plane, as measured by the COBE/DIRBE, COBE/FIRAS, IRTS/MIRS, and IRTS/NIRS instruments. The model has 60 × 10-6 of C (relative to H) locked up in PAHs, with 45 × 10-6 of C in a component peaking at ~6 Å (NC ≈ 100 carbon atoms) to account for the PAH emission features and with 15 × 10-6 of C in a component peaking at ~50 Å to account for the 60 μm flux. The total infrared emission is in excellent agreement with COBE/DIRBE observations at high Galactic latitudes, just as the albedo for our grain model is in accord with observations of the diffuse Galactic light. The aromatic absorption features at 3.3 and 6.2 μm predicted by our dust model are consistent with observations. We calculate infrared emission spectra for our dust model heated by a range of starlight intensities, from 0.3 to 104 times the local interstellar radiation field, and we tabulate the intensities integrated over the SIRTF/IRAC and MIPS bands. We also provide dust opacities tabulated from the extreme-ultraviolet to submillimeter wavelengths.

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Photodissociation regions. I - Basic model. II - A model for the Orion photodissociation region

1985-04-01

A. G. G. M. Tielens , D. J. Hollenbach

view Abstract Citations (1312) References (88) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photodissociation regions. I. Basic model. Tielens, A. G. G. M. ; Hollenbach, D. Abstract … view Abstract Citations (1312) References (88) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photodissociation regions. I. Basic model. Tielens, A. G. G. M. ; Hollenbach, D. Abstract A theoretical parameter study of the temperature and chemical structure of dense photodissociation regions and their resultant spectrum is presented. Models are discussed which are relevant not only to the dust and gas between molecular clouds and H II regions, but also apply to any neutral cloud illuminated by intense FUV fluxes. The models relate observed line and continuum emission from these regions to physical parameters such as the gas density and temperature, the elemental and chemical abundances, the local radiation field, and the grain properties. The results are applied to observational data from the OMC-1 region. The model shows that the observed high brightness temperature of the C I 609 microns line can be explained by emission from the C(+)/C/CO transition region. This difference with previous chemical models is due to a higher gas phase elemental abundance of carbon, to the charge exchange reactions of C(+) with S and SiO, and to carbon self-shielding. Publication: The Astrophysical Journal Pub Date: April 1985 DOI: 10.1086/163111 Bibcode: 1985ApJ...291..722T Keywords: Astronomical Models; Gas Ionization; Molecular Clouds; Nebulae; Photodissociation; Abundance; Brightness Temperature; Emission Spectra; Far Ultraviolet Radiation; Fine Structure; Gas Density; Gas Temperature; H Ii Regions; Infrared Spectra; Astrophysics full text sources ADS | data products SIMBAD (5) NED (1) Related Materials (1) Part 2: 1985ApJ...291..747T

Dynamics of binary-disk interaction. 1: Resonances and disk gap sizes

1994-02-01

Pawel Artymowicz , Stephen H. Lubow

view Abstract Citations (1062) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dynamics of Binary-Disk Interaction. I. Resonances and Disk Gap Sizes Artymowicz, Pawel ; Lubow, … view Abstract Citations (1062) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dynamics of Binary-Disk Interaction. I. Resonances and Disk Gap Sizes Artymowicz, Pawel ; Lubow, Stephen H. Abstract We investigate the gravitational interaction of a generally eccentric binary star system with circumbinary and circumstellar gaseous disks. The disks are assumed to be coplanar with the binary, geometrically thin, and primarily governed by gas pressure and (turbulent) viscosity but not self-gravity. Both ordinary and eccentric Lindblad resonances are primarily responsible for truncating the disks in binaries with arbitrary eccentricity and nonextreme mass ratio. Starting from a smooth disk configuration, after the gravitational field of the binary truncates the disk on the dynamical timescale, a quasi-equilibrium is achieved, in which the resonant and viscous torques balance each other and any changes in the structure of the disk (e.g., due to global viscous evolution) occur slowly, preserving the average size of the gap. We analytically compute the approximate sizes of disks (or disk gaps) as a function of binary mass ratio and eccentricity in this quasi-equilibrium. Comparing the gap sizes with results of direct simulations using the smoothed particle hydrodynamics (SPH), we obtain a good agreement. As a by-product of the computations, we verify that standard SPH codes can adequately represent the dynamics of disks with moderate viscosity, Reynolds number R approximately 103. For typical viscous disk parameters, and with a denoting the binary semimajor axis, the inner edge location of a circumbinary disk varies from 1.8a to 2.6a with binary eccentricity increasing from 0 to 0.25. For eccentricities 0 less than e less than 0.75, the minimum separation between a component star and the circumbinary disk inner edge is greater than a. Our calculations are relevant, among others, to protobinary stars and the recently discovered T Tau pre-main-sequence binaries. We briefly examine the case of a pre-main-sequence spectroscopic binary GW Ori and conclude that circumbinary disk truncation to the size required by one proposed spectroscopic model cannot be due to Linblad resonances, even if the disk is nonviscous. Publication: The Astrophysical Journal Pub Date: February 1994 DOI: 10.1086/173679 Bibcode: 1994ApJ...421..651A Keywords: Accretion Disks; Binary Stars; Orbital Resonances (Celestial Mechanics); Pre-Main Sequence Stars; Stellar Envelopes; Stellar Gravitation; Stellar Mass Accretion; Stellar Systems; Astronomical Spectroscopy; Stellar Models; Stellar Spectra; Astrophysics; ACCRETION; ACCRETION DISKS; STARS: BINARIES: CLOSE; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (1)

Rapid planetesimal formation in turbulent circumstellar disks

2007-08-01

Anders Johansen , Jeffrey S. Oishi , Mordecai‐Mark Mac Low +3 more

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Metallicity Calibrations and the Mass‐Metallicity Relation for Star‐forming Galaxies

2008-07-10

Lisa J. Kewley , Sara L. Ellison

We investigate the effect of metallicity calibrations, AGN classification, and aperture covering fraction on the local mass-metallicity (M-Z) relation using 27,730 star-forming galaxies from the SDSS Data Release 4. We … We investigate the effect of metallicity calibrations, AGN classification, and aperture covering fraction on the local mass-metallicity (M-Z) relation using 27,730 star-forming galaxies from the SDSS Data Release 4. We analyze the SDSS M-Z relation with 10 metallicity calibrations, including theoretical and empirical methods. We show that the choice of metallicity calibration has a significant effect on the shape and y-intercept [12 + log (O/H) ] of the M-Z relation. The absolute metallicity scale (y-intercept) varies up to Δ [ log (O/H) ] = 0.7 dex, depending on the calibration used, and the change in shape is substantial. These results indicate that it is critical to use the same metallicity calibration when comparing different luminosity-metallicity or M-Z relations. We present new metallicity conversions that allow metallicities that have been derived using different strong-line calibrations to be converted to the same base calibration. These conversions facilitate comparisons between different samples, particularly comparisons between galaxies at different redshifts for which different suites of emission lines are available. Our new conversions successfully remove the large 0.7 dex discrepancies between the metallicity calibrations, and we reach agreement in the M-Z relation to within 0.03 dex on average. We investigate the effect of AGN classification and aperture covering fraction on the M-Z relation. We find that different AGN classification methods have negligible effect on the SDSS M-Z relation. We compare the SDSS M-Z relation with nuclear and global relations from the NFGS. The turnover of the M-Z relation at M* ∼ 1010 M☉ depends on the aperture covering fraction. We find that a lower redshift limit of z < 0.04 is insufficient for avoiding aperture effects in fiber spectra of the highest stellar mass (M* > 1010 M☉) galaxies.

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Spectral Energy Distributions of T Tauri Stars with Passive Circumstellar Disks

1997-11-20

Eugene Chiang , Peter Goldreich

We derive hydrostatic, radiative equilibrium models for passive disks surrounding T Tauri stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer reemits directly … We derive hydrostatic, radiative equilibrium models for passive disks surrounding T Tauri stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer reemits directly to space about half the stellar energy it absorbs. The other half is emitted inward and regulates the interior temperature of the disk. The heated disk flares. As a consequence, it absorbs more stellar radiation, especially at large radii, than a flat disk would. The portion of the spectral energy distribution contributed by the disk is fairly flat throughout the thermal infrared. At fixed frequency, the contribution from the surface layer exceeds that from the interior by about a factor 3 and is emitted at more than an order of magnitude greater radius. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on.

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Star Formation in Molecular Clouds: Observation and Theory

1987-09-01

Frank H. Shu , Fred C. Adams , Susana Lizano

Star-formation (SF) processes occurring on the scale of giant molecular clouds (10 to the 6th solar masses and 10 to the 20th cm) or smaller are discussed, reviewing the results … Star-formation (SF) processes occurring on the scale of giant molecular clouds (10 to the 6th solar masses and 10 to the 20th cm) or smaller are discussed, reviewing the results of recent theoretical and observational investigations. Topics examined include the origin of stellar masses; bimodal SF; initial mass functions; binary stars, bound clusters, and hierarchical fragmentation; and the efficiency of SF. The properties of molecular clouds and the origin of substructures in molecular clumps are explored in detail, and consideration is given to gravitational collapse and protostars, bipolar outflows from young stellar objects, visible young stellar objects, and the implications for binary-star and planetary-system formation.

Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds

1998-06-20

David J. Schlegel , Douglas P. Finkbeiner , Marc Davis

We present a full-sky 100 μm map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the … We present a full-sky 100 μm map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 and 240 μm data, we have constructed a map of the dust temperature so that the 100 μm map may be converted to a map proportional to dust column density. The dust temperature varies from 17 to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high-latitude regions, the dust map correlates well with maps of H I emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of H I emission toward denser clouds and of formation of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in dust emission, as expected.

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Star Formation in the Milky Way and Nearby Galaxies

2012-08-28

Robert C. Kennicutt , Neal J. Evans

We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and … We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star formation rates are discussed, and updated prescriptions for calculating star formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

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INTERSTELLAR ABUNDANCES FROM ABSORPTION-LINE OBSERVATIONS WITH THE HUBBLE SPACE TELESCOPE

1996-09-01

Blair D. Savage , Kenneth R. Sembach

▪ Abstract The Goddard High-Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) has yielded precision abundance results for a range of interstellar environments, including gas in the local medium, … ▪ Abstract The Goddard High-Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) has yielded precision abundance results for a range of interstellar environments, including gas in the local medium, in the warm neutral medium, in cold diffuse clouds, and in distant halo clouds. Through GHRS studies, investigators have determined the abundances of elements such as C, N, O, Mg, Si, S, and Fe in individual interstellar clouds. These studies have provided new information about the composition of interstellar dust grains, the origin of the Galactic high-velocity cloud system, and the processes that transport gas between the disk and the halo. Precision measurements of the interstellar D to H ratio and of the abundances of r- and s-process elements have also provided fiducial reference values for cosmological and stellar evolutionary observations and theoretical models.

THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES

2009-03-11

Neal J. Evans , Michael M. Dunham , J. K. Jørgensen +7 more

(Abridged) The c2d Spitzer Legacy project obtained images and photometry with both IRAC and MIPS instruments for five large, nearby molecular clouds. This paper combines information drawn from studies of … (Abridged) The c2d Spitzer Legacy project obtained images and photometry with both IRAC and MIPS instruments for five large, nearby molecular clouds. This paper combines information drawn from studies of individual clouds into a combined and updated statistical analysis of star formation rates and efficiencies, numbers and lifetimes for SED classes, and clustering properties. Current star formation efficiencies range from 3% to 6%. Taken together, the five clouds are producing about 260 solar masses of stars per Myr. The star formation surface density is more than an order of magnitude larger than would be predicted from the Kennicutt relation used in extragalactic studies. Measured against the dense gas probed by the maps of dust continuum emission, the efficiencies are much higher, and the current stock of dense cores would be exhausted in 1.8 Myr on average. The derived lifetime for the Class I phase is 0.44 to 0.54 Myr, considerably longer than some estimates. Similarly, the lifetime for the Class 0 SED class, 0.10 to 0.16 Myr, is longer than early estimates. The great majority (90%) of young stars lie within loose clusters with at least 35 members and a stellar density of 1 solar mass per cubic pc. Accretion at the sound speed from an isothermal sphere over the lifetime derived for the Class I phase could build a star of about 0.25 solar masses, given an efficiency of 0.3. Our data confirm and aggravate the "luminosity problem" for protostars. Our results strongly suggest that accretion is time variable, with prolonged periods of very low accretion. Based on a very simple model and this sample of sources, half the mass of a star would be accreted during only 7% of the Class I lifetime, as represented by the eight most luminous objects.

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A computer program for fast non-LTE analysis of interstellar line spectra

2007-04-03

F. F. S. van der Tak , J. H. Black , F. L. Schöier +2 more

The large quantity and high quality of modern radio and infrared line observations require efficient modeling techniques to infer physical and chemical parameters such as temperature, density, and molecular abundances. … The large quantity and high quality of modern radio and infrared line observations require efficient modeling techniques to infer physical and chemical parameters such as temperature, density, and molecular abundances. We present a computer program to calculate the intensities of atomic and molecular lines produced in a uniform medium, based on statistical equilibrium calculations involving collisional and radiative processes and including radiation from background sources. Optical depth effects are treated with an escape probability method. The program is available on the World Wide Web at http://www.sron.rug.nl/~vdtak/radex/index.shtml . The program makes use of molecular data files maintained in the Leiden Atomic and Molecular Database (LAMDA), which will continue to be improved and expanded. The performance of the program is compared with more approximate and with more sophisticated methods. An Appendix provides diagnostic plots to estimate physical parameters from line intensity ratios of commonly observed molecules. This program should form an important tool in analyzing observations from current and future radio and infrared telescopes.

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Interstellar Dust and Extinction

1990-09-01

John S. Mathis

The ultraviolet (UV) region of the spectrum has been crucial in providing information on the nature of the material and size distribution of the particles of interstellar dust. Before there … The ultraviolet (UV) region of the spectrum has been crucial in providing information on the nature of the material and size distribution of the particles of interstellar dust. Before there were any measurements of the UV properties of interstellar extinction, interstellar particles were believed to be composed primarily of dirty ices. The maximum of the interstellar extinction was believed to be at 0.3 μm, the shortest wavelength then observable. Both of these predictions were quite wrong (as are probably many of our present ideas regarding dust). The first rocket measurement (Stecher, 1965) showed that there is a very strong extinction feature at 0.22 μm. Now we also know the extinction increases dramatically towards the shortest wavelengths which can be reliably measured to date.

Theory of Star Formation

2007-06-25

Christopher F. McKee , Eve C. Ostriker

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a … We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation -- turbulence, magnetic fields, and self-gravity -- are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.

Formation of the Giant Planets by Concurrent Accretion of Solids and Gas

1996-11-01

James B. Pollack , O. Hubickyj , Peter Bodenheimer +3 more

Rotating Nuclear Rings and Extreme Starbursts in Ultraluminous Galaxies

1998-11-10

D. Downes , P. M. Solomon

New CO interferometer data show that the molecular gas in infrared ultraluminous galaxies is in rotating nuclear disks or rings. The CO maps yield disk radii, kinematic major axes, rotation … New CO interferometer data show that the molecular gas in infrared ultraluminous galaxies is in rotating nuclear disks or rings. The CO maps yield disk radii, kinematic major axes, rotation speeds, enclosed dynamical masses, and gas masses. The CO brightness temperatures, the double-peaked CO line profiles, the limits on thermal continuum flux from dust, and the constraint that the gas mass must be less than the dynamical mass all indicate that the CO lines are subthermally excited and moderately opaque (τ = 4 to 10). We fit kinematic models in which most of the CO flux comes from a moderate-density warm intercloud medium, rather than from self-gravitating clouds. Typical ring radii are 300 to 800 pc. We derive gas masses not from a standard CO-to-mass ratio, but from a model of radiative transfer through subthermally excited CO in the molecular disks. This model yields gas masses of ~5 × 109 M☉, ~5 times lower than the standard method, and a ratio M/L ≈ 0.8 M☉ (K km s-1 pc2)-1. In the nuclear disks, we derive a ratio of gas to dynamical mass of Mgas/Mdyn ≈ 1/6, and a maximum ratio of gas to total mass surface density, μ/μtot, of 1/3. For the galaxies VII Zw 31, Arp 193, and IRAS 10565+2448, the CO position-velocity diagrams provide good evidence for rotating molecular rings with a central gap. In addition to the rotating central rings or disks, a new class of star formation region is identified, which we call an extreme starburst. These have a characteristic sizes of only 100 pc, with about 109 M☉ of gas and an IR luminosity of ≈ 3 × 1011 L☉ from recently formed OB stars. Four extreme starbursts are identified in the 3 closest galaxies in the sample, including Arp 220, Arp 193, and Mrk 273. These are the most prodigious star formation events in the local universe, each representing about 1000 times as many OB stars as 30 Doradus. In Mrk 231, the CO (2-1) velocity diagram along the line of nodes shows a 12 diameter inner disk and a 3'' diameter outer disk. The narrow CO line width, the single-peak line profile, the equality of the major and minor axes, and the observed velocity gradients all imply that the molecular disk is nearly face-on, yielding low optical and UV extinction to the active galactic nucleus (AGN). Such a geometry means that the molecular disk cannot be heated by the AGN; the far-infrared (FIR) luminosity of Mrk 231 is powered by a starburst, not the AGN. In Mrk 273, the CO (1-0) maps show long streamers of radius 5 kpc (7'') with velocity gradients north-south, and a nuclear disk of radius 400 pc (06) with velocity gradients east-west. The nuclear disk contains a bright CO core of radius 120 pc (02). In Arp 220, the CO and 1.3 mm continuum maps show the two "nuclei" embedded in a central ring or disk at P.A. 50° and a fainter structure extending 7'' (3 kpc) to the east, normal to the nuclear disk. Models of the CO and dust flux indicate that the two K-band sources contain high-density gas, with n(H2) = 2 × 104 cm-3. There is no evidence that these sources really are the premerger nuclei. They are more likely to be compact extreme starburst regions, containing 109 M☉ of dense molecular gas and new stars, but no old stars. Most of the HCN emission arises in the two nuclei. The luminosity-to-mass ratios for the CO sources in Arp 220 are compatible with the early phases of compact starbursts. There is a large mass of molecular gas currently forming stars with plenty of ionizing photons, and no obvious AGN. The entire bolometric luminosity of Arp 220 comes from starbursts, not an AGN. The CO maps show that the gas in ultraluminous IR galaxies is in extended disks that cannot intercept all the power of central AGNs, even if they exist. We conclude that in ultraluminous IR galaxies—even in Mrk 231, which hosts a quasar—the FIR luminosity is powered by extreme starbursts in the molecular rings or disks, not by dust-enshrouded quasars.

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The CO-to-H2 Conversion Factor

2013-06-29

Alberto D. Bolatto , M. G. Wolfire , Adam K. Leroy

CO line emission represents the most accessible and widely used tracer of the molecular interstellar medium. This renders the translation of observed CO intensity into total H2 gas mass critical … CO line emission represents the most accessible and widely used tracer of the molecular interstellar medium. This renders the translation of observed CO intensity into total H2 gas mass critical to understand star formation and the interstellar medium in our Galaxy and beyond. We review the theoretical underpinning, techniques, and results of efforts to estimate this CO-to-H2 "conversion factor," Xco, in different environments. In the Milky Way disk, we recommend a conversion factor Xco = 2x10^{20} cm^-2/(K km/s)^-1 with +/-30% uncertainty. Studies of other "normal galaxies" return similar values in Milky Way-like disks, but with greater scatter and systematic uncertainty. Departures from this Galactic conversion factor are both observed and expected. Dust-based determinations, theoretical arguments, and scaling relations all suggest that Xco increases with decreasing metallicity, turning up sharply below metallicity ~1/3-1/2 solar in a manner consistent with model predictions that identify shielding as a key parameter. Based on spectral line modeling and dust observations, Xco appears to drop in the central, bright regions of some but not all galaxies, often coincident with regions of bright CO emission and high stellar surface density. This lower Xco is also present in the overwhelmingly molecular interstellar medium of starburst galaxies, where several lines of evidence point to a lower CO-to-H2 conversion factor. At high redshift, direct evidence regarding the conversion factor remains scarce; we review what is known based on dynamical modeling and other arguments.

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Interstellar Polycyclic Aromatic Hydrocarbon Molecules

2008-08-15

A. G. G. M. Tielens

Large polycyclic aromatic hydrocarbon (PAH) molecules carry the infrared (IR) emission features that dominate the spectra of most galactic and extragalactic sources. This review surveys the observed mid-IR characteristics of … Large polycyclic aromatic hydrocarbon (PAH) molecules carry the infrared (IR) emission features that dominate the spectra of most galactic and extragalactic sources. This review surveys the observed mid-IR characteristics of these emission features and summarizes laboratory and theoretical studies of the spectral characteristics of PAHs and the derived intrinsic properties of emitting interstellar PAHs. Dedicated experimental studies have provided critical input for detailed astronomical models that probe the origin and evolution of interstellar PAHs and their role in the universe. The physics and chemistry of PAHs are discussed, emphasizing the contribution of these species to the photoelectric heating and the ionization balance of the interstellar gas and to the formation of small hydrocarbon radicals and carbon chains. Together, these studies demonstrate that PAHs are abundant, ubiquitous, and a dominant force in the interstellar medium of galaxies.

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HI4PI: a full-sky H i survey based on EBHIS and GASS

2016-10-01

N. Ben Bekhti , L. Flöer , Reinhard Keller +7 more

Measurement of the Galactic neutral atomic hydrogen (HI) column density, NHI, and brightness temperatures, Tb, is of high scientific value for a broad range of astrophysical disciplines. In the past … Measurement of the Galactic neutral atomic hydrogen (HI) column density, NHI, and brightness temperatures, Tb, is of high scientific value for a broad range of astrophysical disciplines. In the past two decades, one of the most-used legacy HI datasets has been the Leiden/Argentine/Bonn Survey (LAB). We release the HI 4$\pi$ survey (HI4PI), an all-sky database of Galactic HI, which supersedes the LAB survey. The HI4PI survey is based on data from the recently completed first coverage of the Effelsberg-Bonn HI Survey (EBHIS) and from the third revision of the Galactic All-Sky Survey (GASS). EBHIS and GASS share similar angular resolution and match well in sensitivity. Combined, they are ideally suited to be a successor to LAB. The new HI4PI survey outperforms the LAB in angular resolution (16.2', FWHM) and sensitivity (RMS: 43 mK). Moreover, it has full spatial sampling and thus overcomes a major drawback of LAB, which severely undersamples the sky. We publish all-sky column density maps of the neutral atomic hydrogen in the Milky Way, along with full spectroscopic data, in several map projections including HEALPix.

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Cooling Flows in Clusters of Galaxies

1994-09-01

A. C. Fabian

The cooling time in the dense gas within 50 – 300 kpc of the central galaxy in most clusters is found from X-ray images to be less than about 1010 … The cooling time in the dense gas within 50 – 300 kpc of the central galaxy in most clusters is found from X-ray images to be less than about 1010 yr. The weight of the overlying gas then causes a net inflow which is called a cooling flow. X-ray spectra confirm that the gas is cooling and loses at least 90 per cent of its thermal energy. The rate at which the gas cools ranges from ~ 10 – 500 M⊙ yr−1 . The soft X-ray absorption now discovered in cooling flows suggests that the cooled gas accumulates as very cold, small, gas clouds. Any large-scale star formation must be biased to low mass objects, except in the centres of some flows where some massive star may form, possibly from larger clouds assembled from cloud collisions and aggregation.

Stellar Multiplicity

2013-06-29

Gaspard Duchêne , Adam L. Kraus

Stellar multiplicity is a ubiquitous outcome of the star-formation process. The frequency and main characteristics of multiple systems, and their dependence on primary mass and environment, are powerful tools to … Stellar multiplicity is a ubiquitous outcome of the star-formation process. The frequency and main characteristics of multiple systems, and their dependence on primary mass and environment, are powerful tools to probe this process. Although early attempts were fraught with selection biases and limited completeness, instrumentation breakthroughs in the past two decades now enable robust statistical analyses. In this review, we summarize current empirical knowledge of stellar multiplicity for main sequence stars and brown dwarfs, as well as among populations of pre-main-sequence stars and embedded protostars. Among field objects, the multiplicity rate and breadth of the orbital period distribution are steep functions of the primary mass, whereas the mass ratio distribution is essentially flat for most populations other than the lowest mass objects. The time-variation of the frequency of visual companions follows two parallel, constant tracks corresponding to loose and dense stellar populations, although current observations do not yet distinguish whether initial multiplicity properties are universal or dependent on the physical conditions of the parent cloud. Nonetheless, these quantitative trends provide a rich comparison basis for numerical and analytical models of star formation.

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THE STAR FORMATION EFFICIENCY IN NEARBY GALAXIES: MEASURING WHERE GAS FORMS STARS EFFECTIVELY

2008-11-19

Adam K. Leroy , Fabian Walter , E. Brinks +4 more

We measure the star formation efficiency (SFE), the star formation rate (SFR) per unit of gas, in 23 nearby galaxies and compare it with expectations from proposed star formation laws … We measure the star formation efficiency (SFE), the star formation rate (SFR) per unit of gas, in 23 nearby galaxies and compare it with expectations from proposed star formation laws and thresholds. We use H i maps from The H i Nearby Galaxy Survey (THINGS) and derive H2 maps of CO measured by HERA CO-Line Extragalactic Survey and Berkeley-Illinois-Maryland Association Survey of Nearby Galaxies. We estimate the SFR by combining Galaxy Evolution Explorer (GALEX) far-ultraviolet maps and the Spitzer Infrared Nearby Galaxies Survey (SINGS) 24 μm maps, infer stellar surface density profiles from SINGS 3.6 μm data, and use kinematics from THINGS. We measure the SFE as a function of the free fall and orbital timescales, midplane gas pressure, stability of the gas disk to collapse (including the effects of stars), the ability of perturbations to grow despite shear, and the ability of a cold phase to form. In spirals, the SFE of H2 alone is nearly constant at (5.25 ± 2.5) × 10−10 yr−1 (equivalent to an H2 depletion time of 1.9 × 109 yr) as a function of all of these variables at our 800 pc resolution. Where the interstellar medium (ISM) is mostly H i, however, the SFE decreases with increasing radius in both spiral and dwarf galaxies, a decline reasonably described by an exponential with scale length 0.2r25–0.25r25. We interpret this decline as a strong dependence of giant molecular cloud (GMC) formation on environment. The ratio of molecular-to-atomic gas appears to be a smooth function of radius, stellar surface density, and pressure spanning from the H2-dominated to H i-dominated ISM. The radial decline in SFE is too steep to be reproduced only by increases in the free-fall time or orbital time. Thresholds for large-scale instability suggest that our disks are stable or marginally stable and do not show a clear link to the declining SFE. We suggest that ISM physics below the scales that we observe—phase balance in the H i, H2 formation and destruction, and stellar feedback—governs the formation of GMCs from H i.

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The Milky Way in Molecular Clouds: A New Complete CO Survey

2001-02-01

T. M. Dame , Dap Hartmann , P. Thaddeus

New large-scale CO surveys of the first and second Galactic quadrants and the nearby molecular cloud complexes in Orion and Taurus, obtained with the CfA 1.2 m telescope, have been … New large-scale CO surveys of the first and second Galactic quadrants and the nearby molecular cloud complexes in Orion and Taurus, obtained with the CfA 1.2 m telescope, have been combined with 31 other surveys obtained over the past two decades with that instrument and a similar telescope on Cerro Tololo in Chile, to produce a new composite CO survey of the entire Milky Way. The survey consists of 488,000 spectra that Nyquist or beamwidth ( °) sample the entire Galactic plane over a strip 4°-10° wide in latitude, and beamwidth or ° sample nearly all large local clouds at higher latitudes. Compared with the previous composite CO survey of Dame et al. (1987), the new survey has 16 times more spectra, up to 3.4 times higher angular resolution, and up to 10 times higher sensitivity per unit solid angle. Each of the component surveys was integrated individually using clipping or moment masking to produce composite spatial and longitude-velocity maps of the Galaxy that display nearly all of the statistically significant emission in each survey but little noise.

Galactic Stellar and Substellar Initial Mass Function

2003-07-01

G. Chabrier

We review recent determinations of the present‐day mass function (PDMF) and initial mass function (IMF) in various components of the Galaxy—disk, spheroid, young, and globular clusters—and in conditions characteristic of … We review recent determinations of the present‐day mass function (PDMF) and initial mass function (IMF) in various components of the Galaxy—disk, spheroid, young, and globular clusters—and in conditions characteristic of early star formation. As a general feature, the IMF is found to depend weakly on the environment and to be well described by a power‐law form for m≳1 M⊙ and a lognormal form below, except possibly for early star formation conditions. The disk IMF for single objects has a characteristic mass around mc ∼ 0.08 M⊙ and a variance in logarithmic mass σ ∼ 0.7, whereas the IMF for multiple systems has mc ∼ 0.2 M⊙ and σ ∼ 0.6. The extension of the single MF into the brown dwarf regime is in good agreement with present estimates of L‐ and T‐dwarf densities and yields a disk brown dwarf number density comparable to the stellar one, nBD ∼ n* ∼ 0.1 pc−3. The IMF of young clusters is found to be consistent with the disk field IMF, providing the same correction for unresolved binaries, confirming the fact that young star clusters and disk field stars represent the same stellar population. Dynamical effects, yielding depletion of the lowest mass objects, are found to become consequential for ages ≳130 Myr. The spheroid IMF relies on much less robust grounds. The large metallicity spread in the local subdwarf photometric sample, in particular, remains puzzling. Recent observations suggest that there is a continuous kinematic shear between the thick‐disk population, present in local samples, and the genuine spheroid one. This enables us to derive only an upper limit for the spheroid mass density and IMF. Within all the uncertainties, the latter is found to be similar to the one derived for globular clusters and is well represented also by a lognormal form with a characteristic mass slightly larger than for the disk, mc ∼ 0.2–0.3 M⊙, excluding a significant population of brown dwarfs in globular clusters and in the spheroid. The IMF characteristic of early star formation at large redshift remains undetermined, but different observational constraints suggest that it does not extend below ∼1 M⊙. These results suggest a characteristic mass for star formation that decreases with time, from conditions prevailing at large redshift to conditions characteristic of the spheroid (or thick disk) to present‐day conditions. These conclusions, however, remain speculative, given the large uncertainties in the spheroid and early star IMF determinations.

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Disk Frequencies and Lifetimes in Young Clusters

2001-06-01

Karl E. Haisch , Elizabeth A. Lada , C. J. Lada

We report the results of the first sensitive L-band survey of the intermediate-age (2.5-30 Myr) clusters NGC 2264, NGC 2362, and NGC 1960. We use JHKL colors to obtain a … We report the results of the first sensitive L-band survey of the intermediate-age (2.5-30 Myr) clusters NGC 2264, NGC 2362, and NGC 1960. We use JHKL colors to obtain a census of the circumstellar disk fractions in each cluster. We find disk fractions of 52% ± 10%, 12% ± 4%, and 3% ± 3% for the three clusters, respectively. Together with our previously published JHKL investigations of the younger NGC 2024, Trapezium, and IC 348 clusters, we have completed the first systematic and homogeneous survey for circumstellar disks in a sample of young clusters that both span a significant range in age (0.3-30 Myr) and contain statistically significant numbers of stars whose masses span nearly the entire stellar mass spectrum. Analysis of the combined survey indicates that the cluster disk fraction is initially very high (≥80%) and rapidly decreases with increasing cluster age, such that one-half the stars within the clusters lose their disks in ≲3 Myr. Moreover, these observations yield an overall disk lifetime of ~6 Myr in the surveyed cluster sample. This is the timescale for essentially all the stars in a cluster to lose their disks. This should set a meaningful constraint for the planet-building timescale in stellar clusters. The implications of these results for current theories of planet formation are briefly discussed.

Embedded Clusters in Molecular Clouds

2003-09-01

C. J. Lada , Elizabeth A. Lada

▪ Abstract Stellar clusters are born embedded within giant molecular clouds (GMCs) and during their formation and early evolution are often only visible at infrared wavelengths, being heavily obscured by … ▪ Abstract Stellar clusters are born embedded within giant molecular clouds (GMCs) and during their formation and early evolution are often only visible at infrared wavelengths, being heavily obscured by dust. Over the past 15 years advances in infrared detection capabilities have enabled the first systematic studies of embedded clusters in galactic molecular clouds. In this article we review the current state of empirical knowledge concerning these extremely young protocluster systems. From a survey of the literature we compile the first extensive catalog of galactic embedded clusters. We use the catalog to construct the mass function and estimate the birthrate for embedded clusters within ∼2 kpc of the sun. We find that the embedded cluster birthrate exceeds that of visible open clusters by an order of magnitude or more indicating a high infant mortality rate for protocluster systems. Less than 4–7% of embedded clusters survive emergence from molecular clouds to become bound clusters of Pleiades age. The vast majority (90%) of stars that form in embedded clusters form in rich clusters of 100 or more members with masses in excess of 50 M ⊙ . Moreover, observations of nearby cloud complexes indicate that embedded clusters account for a significant (70–90%) fraction of all stars formed in GMCs. We review the role of embedded clusters in investigating the nature of the initial mass function (IMF) that, in one nearby example, has been measured over the entire range of stellar and substellar mass, from OB stars to substellar objects near the deuterium burning limit. We also review the role embedded clusters play in the investigation of circumstellar disk evolution and the important constraints they provide for understanding the origin of planetary systems. Finally, we discuss current ideas concerning the origin and dynamical evolution of embedded clusters and the implications for the formation of bound open clusters.

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Interstellar Dust Grains

2003-09-01

B. T. Draine

▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical luminescence; infrared emission; microwave emission; … ▪ Abstract This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical luminescence; infrared emission; microwave emission; optical, UV, and X-ray scattering by dust; and polarization of starlight and of infrared emission. The relationship between presolar grains in meteorites and the interstellar grain population is discussed. Candidate grain materials and abundance constraints are considered. A dust model consisting of amorphous silicate grains, graphite grains, and polycyclic aromatic hydrocarbons is compared with observed emission and scattering. Some issues concerning evolution of interstellar dust are discussed.

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Protostars and Planets IV

2000-01-01

V. Mannings

HerschelSpace Observatory

2010-07-01

G. Pilbratt , J. R. Riedinger , Thomas Passvogel +7 more

Herschel was launched on 14 May 2009, and is now an operational ESA space observatory offering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55-671 {\mu}m. Herschel carries … Herschel was launched on 14 May 2009, and is now an operational ESA space observatory offering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55-671 {\mu}m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

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A Quantitative Comparison of the Small Magellanic Cloud, Large Magellanic Cloud, and Milky Way Ultraviolet to Near‐Infrared Extinction Curves

2003-08-20

Karl D. Gordon , Geoffrey C. Clayton , K. A. Misselt +2 more

We present an exhaustive, quantitative comparison of all of the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior … We present an exhaustive, quantitative comparison of all of the known extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with our understanding of the general behavior of Milky Way extinction curves. The R_V dependent CCM relationship and the sample of extinction curves used to derive this relationship is used to describe the general behavior of Milky Way extinction curves. The ultraviolet portion of the SMC and LMC extinction curves are derived from archival IUE data, except for one new SMC extinction curve which was measured using HST/STIS observations. The optical extinction curves are derived from new (for the SMC) and literature UBVRI photometry (for the LMC). The near-infrared extinction curves are calculated mainly from 2MASS photometry supplemented with DENIS and new JHK photometry. For each extinction curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust column as the extinction curve. We compare the properties of the SMC and LMC extinction curves with the CCM relationship three different ways: each curve by itself, the behavior of extinction at different wavelengths with R_V, and behavior of the extinction curve FM fit parameters with R_V. As has been found previously, we find that a small number of LMC extinction curves are consistent with the CCM relationship, but majority of the LMC and all of the SMC curves do not follow the CCM relationship. For the first time, we find that the CCM relationship seems to form a bound on the properties of all of the LMC and SMC extinction curves. This result strengthens the picture of dust extinction curves exhibit a continuum of properties between those found in the Milky Way and the SMC Bar. (abridged)

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Oort Cloud Formation and Evolution in Star Clusters

2025-06-25

Justine C. Obidowski , Jeremy J. Webb , Simon Portegies Zwart +1 more | The Astrophysical Journal

Abstract It is unknown whether an Oort cloud reaches its maximum mass within its star’s birth cluster or millions of years later. Complicating the Oort cloud evolution process is the … Abstract It is unknown whether an Oort cloud reaches its maximum mass within its star’s birth cluster or millions of years later. Complicating the Oort cloud evolution process is the fact that comets can be stripped from orbit due to perturbations from passing stars. We explore how a star’s cluster escape time ( t esc ) and the time its Oort cloud reaches maximum mass ( t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) affect the Oort cloud’s ability to survive via N -body simulations. In a 14 M ⊙ pc –3 cluster, we identify 50 stars of 1 M ⊙ with a range of t esc to host Oort clouds, each with 1000 comets at t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> . For each host, we consider Oort clouds that reach maximum mass 0, 50, and 250 Myr after the cluster’s formation. Each Oort cloud’s evolution is simulated in the cluster from t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> to t esc . Only a fraction of comets tend to remain in orbit, with this amount depending on t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> and t esc . We observe that 12%, 22%, and 32% of Oort clouds with a t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> of 0, 50, and 250 Myr retain >50% of their comets at t esc , respectively. We find that the fraction of comets stripped has the relationship <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mo>=</mml:mo> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> <mml:mspace width="0.25em"/> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mfenced close=")" open="(" separators=""> <mml:mrow> <mml:mfrac> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> <mml:msub> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mo form="prefix" movablelimits="true">max</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Myr</mml:mi> </mml:mrow> </mml:mfrac> </mml:mrow> </mml:mfenced> </mml:mrow> </mml:math> , where m = 0.32 ± 0.04, indicating that the longer the Oort cloud remains in the cluster, the more comets are stripped, with this fraction increasing logarithmically at approximately the same rate for each t <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> </mml:math> .

Evidence for a sub-Jovian planet in the young TWA 7 disk

2025-06-25

A.‐M. Lagrange , C. Wilkinson , Mathilde Mâlin +7 more | Nature

Planets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion … Planets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion years, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies1,2. Tens of debris disks, with sizes of tens, sometimes hundreds, of astronomical units have been resolved with high-spatial-resolution, high-contrast imagers at optical and near-infrared or (sub)millimetre interferometers3,4. They commonly show cavities, ring-like structures and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals2,5. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2-10 MJ) of high-contrast imaging instruments (see, for example, refs. 6-9) before the James Webb Space Telescope. Here we have used the unprecedented sensitivity of the James Webb Space Telescope's Mid-Infrared Instrument10,11 in the thermal infrared to search for such planets in the disk of the approximately 6.4-Myr-old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arcsec from the star, which is best interpreted as a cold, sub-Jupiter-mass planet. Its estimated mass (about 0.3 MJ) and position (about 52 AU, de-projected) can thoroughly account for the main disk structures.

Investigating Silicate, Carbon, and Water in the Diffuse Interstellar Medium: The First Shots from WISCI

2025-06-24

S. T. Zeegers , J. P. Marshall , Karl D. Gordon +7 more | The Astrophysical Journal

Abstract The dusty interstellar medium (ISM) of the Milky Way is distributed in a complex, cloudy structure. It is fundamental to the radiation balance within the Milky Way, provides a … Abstract The dusty interstellar medium (ISM) of the Milky Way is distributed in a complex, cloudy structure. It is fundamental to the radiation balance within the Milky Way, provides a reaction surface to form complex molecules, and is the feedstock for future generations of stars and planets. The life cycle of interstellar dust is not completely understood, and neither are its structure nor composition. The abundance, composition, and structure of dust in the diffuse ISM can be determined by combining infrared, optical, and ultraviolet spectroscopy. JWST enables measurement of the faint absorption of ISM dust grains against bright stars at kiloparsec distances across the infrared spectrum. Here we present an overview of the project “Webb Investigation of Silicates, Carbons, and Ices” (WISCI) along with interpretation of two targets, GSC 08152-02121 and CPD-59 5831. Observations of 12 WISCI target stars were taken by JWST, the Hubble Space Telescope, Himalayan Chandra Telescope, and the Very Large Telescope. We use these to characterize the targets’ spectral types and calculate their line-of-sight extinction parameters, A V and R V . We find absorption in the JWST spectra of GSC 08152-02121 and CPD-59 5831 associated with carbonaceous dust around 3.4 and 6.2 μ m and amorphous silicates at 9.7 μ m. In GSC 08152-02121, we also find indications of absorption by trapped water around 3 μ m. This first look from WISCI demonstrates the line-of-sight variability within the sample, and the program’s potential to identify and correlate features across ultraviolet to mid-infrared wavelengths.

Investigating the role of magnetic fields in the formation and evolution of striations in interstellar clouds with the probe far-infrared mission for astrophysics

2025-06-24

R. Skalidis , Konstantinos Tassis , Aris Tritsis +1 more | Journal of Astronomical Telescopes Instruments and Systems

Supersonic Gravitational Collapse for Nonisentropic Gaseous Stars

2025-06-24

Christopher Alexander , Mahir Hadžić , Matthew R. I. Schrecker | SIAM Journal on Mathematical Analysis

Filamentary Hierarchies and Superbubbles. I. Characterizing Filament Properties across a Simulated Spiral Galaxy

2025-06-24

Rachel Pillsworth , Erica Roscoe , Ralph E. Pudritz +1 more | The Astrophysical Journal

Abstract High-resolution surveys reveal that the interstellar medium in the Milky Way and nearby galaxies consists of interlinked hierarchies of filamentary structure and superbubbles extending from galactic to subparsec scales. … Abstract High-resolution surveys reveal that the interstellar medium in the Milky Way and nearby galaxies consists of interlinked hierarchies of filamentary structure and superbubbles extending from galactic to subparsec scales. The characterization of filament properties across this hierarchy is of fundamental importance for the origin of giant molecular clouds and their star clusters. In this paper, we characterize the properties of filaments greater than 25 pc in length that are produced in the multiscale galactic MHD simulations of B. Zhao et al. By adapting the FilFinder algorithm of E. W. Koch & E. W. Rosolowsky, we extract over 500 filaments ranging up to 10 kpc in scale, to derive the probability distribution functions for filament masses and lengths, magnetic field orientations, and the gravitational stability and fragmentation patterns of filaments. We find power-law distributions for filament masses and lengths. The former has a power-law index α m = 1.85 that is nearly identical to that of observed giant molecular cloud (GMC) mass functions in extragalactic and Galactic surveys, suggesting that GMC properties are inherited from their host filaments. The fragmentation of magnetized filaments on 200 pc scales or less occurs when they exceed an average critical line mass, as predicted by theory. On larger scales, however, kiloparsec filaments form out of the cold neutral medium, and fragmentation follows local variations in the critical line mass along spiral arms or at the boundaries of superbubbles.

Dense clumps survive in the vicinity of R136 in 30 Doradus

2025-06-20

M. T. Valdivia-Mena , M. Rubio , V. M. Kalari +5 more | Astronomy and Astrophysics

The young massive cluster R136 at the center of 30 Doradus (30 Dor) in the Large Magellanic Cloud (LMC) generates a cavity in the surrounding molecular cloud. However, there is … The young massive cluster R136 at the center of 30 Doradus (30 Dor) in the Large Magellanic Cloud (LMC) generates a cavity in the surrounding molecular cloud. However, there is molecular gas between 2 and 10 pc in projection from R136's center. The region, known as the Stapler nebula, hosts the closest known molecular gas clouds to R136. We investigated the properties of molecular gas in the Stapler nebula to better understand why these clouds survive so close in projection to R136. We used Atacama Large Millimeter/Sub-millimeter Array 7m observations in Band 7 (345 GHz) of continuum emission, ^12CO and ^13CO, together with dense gas tracers CS, HCO^+, and HCN. Our observations resolve the molecular clouds in the nebula into individual parsec-sized clumps. We determined the physical properties of the clumps using both dust and molecular emission, and compared the emission properties observed close to R136 to other clouds in the LMC. The densest clumps in our sample, where we observe CS, HCO^+, and HCN, are concentrated in a northwest-southeast diagonal seen as a dark dust lane in HST images. Resolved clumps have masses between ∼ 200-2500 and the values obtained using the virial theorem are higher than the masses obtained through ^12CO and ^12CO luminosity. The velocity dispersion of the clumps is due both to self-gravity and to the external pressure of the gas. Clumps at the center of our map, which have detections of dense gas tracers crit ∼10^6 cm^-3 and above), are spatially coincident with young stellar objects. The clumps' physical and chemical properties are consistent with other clumps in 30 Dor. We suggest that these clumps are the densest regions of a molecular cloud carved by the radiation of R136.

Water vapour masers in long-period variable stars. IV. Mira variables R Cas, o Cet and R Leo

2025-06-19

J. Brand , D. Engels , A. Zanichelli +1 more | Astronomy and Astrophysics

We carry out decades-long single-dish monitoring of the variation in water-maser emission associated with the circumstellar envelopes (CSEs) of different types of evolved stars. We follow the variation in the … We carry out decades-long single-dish monitoring of the variation in water-maser emission associated with the circumstellar envelopes (CSEs) of different types of evolved stars. We follow the variation in the maser emission over long time intervals (multiple optical periods) to understand the structure and kinematics of the stellar wind that drives the maser clouds away from the star. We also determine how this may depend on the stellar properties. We carried out monitoring campaigns with single-dish telescopes of water-maser emission at 22 GHz in the CSEs of four stars: o,Cet, R,Leo, χ,Cyg, and R,Cas. The observations took place with some interruptions between 1987 and 2023. The exact time interval differed from one star to the next, but no star was monitored for fewer than 15 years. The variability in integrated flux in the masers in R,Cas and o,Cet followed the variability in the optical with the same period, but with a lag of about one-third in phase. R,Leo was too often below our sensitivity threshold for us to determine a radio period. Remarkably, no maser at all was detected in χ,Cyg. The variability in the masers in R,Cas has a distinctive pattern. The total flux, modulated by the pulsations of the star, gradually increases to a maximum, which is followed by a similar decrease. This takes about 20 years. The pattern is repeated after an interval of quiescence of several years. Our observations have covered about one and a half cycle of this pattern so far. During its decline from a maximum, the variation in the flux resembles a damped harmonic oscillator. There are two dominant emission components that move almost tangentially on either side of the star with respect to the observer. The redshifted component likely originates from a single cloud and seems to be falling back towards the star. The blue component, moving in the CSE hemisphere nearest to us, has no drift in the line-of-sight velocity and appears to originate in a time series of short-living clouds with line-of-sight velocities within ∼ 1 of each other. No systematic velocity drifts are found in R,Leo and o,Cet. A few bursts of emission were detected at infrequent times in R,Cas and R,Leo that lasted about a year and caused an increase in the flux density by $1-2$ orders of magnitude. The velocity range of the maser emission is lsim 10 which is narrower than the majority of the Miras and semi-regular variables we studied so far. In particular, in the stars with a low bolometric luminosity, o,Cet and R,Leo, only the brightest maser components from a limited part of the CSE are visible. The existence of a zone in the CSE with favourable conditions for maser excitation is confirmed most clearly in the case of R,Cas through the unique pattern of its maser variability. The bolometric luminosity of a star and the velocity range of its water-maser emission, that is, the number of emission components in the spectra, are clearly correlated. Most maser components in the CSEs we studied originated in clouds that move almost perpendicular to the line of sight. The redshifted emission in R,Cas is consistent with an origin in a single cloud that lived for at least about eight years.

Numerical simulations of the line-force-driven winds from active galactic nuclei: The special relativistic effects

2025-06-19

Li Tang , Xiao‐Hong Yang , De-Fu Bu | Astronomy and Astrophysics

Ultra-fast outflows (UFOs) with mildly relativistic velocities are frequently observed in active galactic nuclei (AGNs). The line-force-driving mechanism is often taken as a potential mechanism for driving UFOs. Due to … Ultra-fast outflows (UFOs) with mildly relativistic velocities are frequently observed in active galactic nuclei (AGNs). The line-force-driving mechanism is often taken as a potential mechanism for driving UFOs. Due to the line-force-driven winds moving at mildly relativistic velocities, the special relativistic effects become important. There are two special relativistic effects: one is the influence of the disc rotation on the radiation field; the other is the radiation-drag effect. We wish to study the influence of the special relativistic effects on the line-force-driven winds, and we performed numerical simulations to investigate this. We find that the line-force-driven winds are significantly weakened when the special relativistic effects are considered. Compared with the case without special relativistic effects, when special relativistic effects are considered the winds are closer to the disc surface, the maximum speed of winds is reduced by ∼20 percent--70 percent, and the mass outflow rate and the kinetic power is significantly reduced.

Polycyclic Aromatic Hydrocarbons in the circumstellar medium of Herbig Ae/Be stars

2025-06-19

R. Arun , Blesson Mathew , B. Shridharan +4 more | Research in Astronomy and Astrophysics

Abstract We present a comprehensive mid-infrared spectroscopic survey of 124 Herbig Ae/Be stars using newly processed Spitzer/IRS spectra from the newly released CASSISjuice database. Based on prominent dust and molecular … Abstract We present a comprehensive mid-infrared spectroscopic survey of 124 Herbig Ae/Be stars using newly processed Spitzer/IRS spectra from the newly released CASSISjuice database. Based on prominent dust and molecular signatures (polycyclic aromatic hydrocarbons, silicates, and hydrogenated amorphous carbons), we classify the stars into five groups. Our analysis reveals that 64\% of the spectra show PAH emission, with detections peaking in the stellar effective temperature range 7000--11000\,K (B9--A5). Silicate features appear in 50\% of the sample and likewise diminish at higher temperatures. Additionally, we find that future PAH studies can focus on Herbig Ae/Be stars with a spectral index $n_{2-24} > -1$ and flared morphologies to maximize PAH detections. The 6.2μm PAH band is the most frequently observed in our sample, shifting blueward with increasing stellar temperature, and this is the largest sample yet used to test that peak shift. The weaker 6.0μm feature does not shift with 6.2 μm, implying a distinct origin of C=O (carbonyl) or olefinic C=C stretching relative to C--C vibrations. We examined the 11.0/11.2 PAH ratio using high-resolution Spitzer spectra for the first time in a sample of Herbig Ae/Be stars, finding a range of ionization conditions. This study provides a strong foundation for future JWST observations of intermediate-mass pre-main-sequence stars.

Shadow-based Framework for Estimating Transition Disk Geometries

2025-06-19

Ryuta Orihara , Munetake Momose | The Astrophysical Journal

Abstract Some transition disks host misaligned inner disks with radii of several astronomical units. Understanding the geometric and physical properties of these misaligned disks is essential for advancing terrestrial planet … Abstract Some transition disks host misaligned inner disks with radii of several astronomical units. Understanding the geometric and physical properties of these misaligned disks is essential for advancing terrestrial planet formation models. This study introduces a novel method to infer the three-dimensional structures of both inner and outer disks by analyzing nonaxisymmetric shadows and the horizon in optical and infrared scattered light images of the outer disk. This method was applied to the HD 100453 system, in which infrared scattered light images from the Very Large Telescope revealed disk shadows. These results indicate that the inner disk is misaligned by ∼70° relative to the outer disk, which is consistent with the results of previous studies. The aspect ratio of the inner disk surface was estimated to be 0.17, which may reflect the surface height of the optically thick dusty component due to vertical lofting by MHD winds or turbulence. In addition, the surface height distribution of the outer disk was characterized, providing novel insights into its vertical structure.

Detection of Hydrocarbons in the Disk around an Actively Accreting Planetary-mass Object

2025-06-18

Laura Flagg , A. Scholz , V. Almendros-Abad +6 more | The Astrophysical Journal

Abstract We present the 0.6–12 μ m spectrum of Cha 1107-7626, a 6–10 Jupiter-mass free-floating object in the ∼2 Myr-old Chamaeleon-I star-forming region, from observations with the NIRSpec and MIRI … Abstract We present the 0.6–12 μ m spectrum of Cha 1107-7626, a 6–10 Jupiter-mass free-floating object in the ∼2 Myr-old Chamaeleon-I star-forming region, from observations with the NIRSpec and MIRI instruments on board the James Webb Space Telescope. We confirm that Cha 1107-7626 is one of the lowest-mass objects known to harbor a dusty disk with infrared excess emission at wavelengths beyond 4 μ m. Our NIRSpec data and prior ground-based observations provide strong evidence for ongoing accretion through hydrogen recombination lines. In the mid-infrared spectrum, we detect unambiguously emission lines caused by methane (CH 4 ) and ethylene (C 2 H 4 ) in its circumsubstellar disk. Our findings mean that Cha 1107-7626 is by far the lowest-mass object with hydrocarbons observed in its disk. The spectrum of the disk looks remarkably similar to that of ISO-ChaI 147, a very low-mass star with a carbon-rich disk that is 10–20 times more massive than Cha 1107-7626. The hydrocarbon lines can be accounted for with a model assuming gas temperatures of a few hundred kelvin in the inner disk. The obvious similarities between the spectra of a low-mass star and a planetary-mass object indicate that the conditions in the inner disks can be similar across a wide range of central object masses.

Quantifying the Impact of the Dust Torque on the Migration of Low-mass Planets. II. The Role of Pebble Accretion in Planet Growth within a Global Planet Formation Model

2025-06-18

O. M. Guilera , Pablo Benítez-Llambay , M. M. Miller Bertolami +1 more | The Astrophysical Journal

Abstract Although dust constitutes only about 1% of the mass in a protoplanetary disk, recent studies reveal its substantial impact on the torques experienced by low- and intermediate-mass planetary cores. … Abstract Although dust constitutes only about 1% of the mass in a protoplanetary disk, recent studies reveal its substantial impact on the torques experienced by low- and intermediate-mass planetary cores. In this study, we present the first comprehensive analysis of the dust torque’s influence on the evolution of growing planetary embryos as they migrate through a protoplanetary disk and undergo gas and pebble accretion. Our global model incorporates viscous accretion and X-ray photoevaporation effects on the gaseous disk while also accounting for the dynamic processes of dust growth and evolution, including coagulation, drift, and fragmentation. Our findings demonstrate that dust torque significantly affects planetary migration patterns, particularly facilitating prominent outward migration for planets forming within the water-ice line. This outward thrust arises from an enhanced dust-to-gas mass ratio in the inner disk, driven by the inward drift of pebbles from the outer regions. Conversely, for planets that originate beyond the water-ice line, while the dust torque attenuates inward migration, it does not substantially alter their overall migration trajectories. This is attributed to the rapid reduction in dust-to-gas mass ratio, resulting from swift pebble drift and the short formation timescales prevalent in that region. Overall, our findings highlight the critical role of dust torque in shaping the migration of low- and intermediate-mass planets, particularly in conditions where increased dust concentrations amplify its effects. These insights have significant implications for understanding the formation timescales, mass distributions, and compositional characteristics of emerging planetary systems.

Here There Be (Dusty) Monsters: High-redshift Active Galactic Nuclei Are Dustier than Their Hosts

2025-06-17

Madisyn Brooks , Raymond C. Simons , Jonathan R. Trump +7 more | The Astrophysical Journal

Abstract JWST spectroscopy has discovered a population of z ≳ 3.5 galaxies with broad Balmer emission lines and narrow forbidden lines that are consistent with hosting active galactic nuclei (AGN). … Abstract JWST spectroscopy has discovered a population of z ≳ 3.5 galaxies with broad Balmer emission lines and narrow forbidden lines that are consistent with hosting active galactic nuclei (AGN). Many of these systems, now known as “little red dots,” are compact and have unique colors that are very red in the optical/near-infrared and blue in the ultraviolet. The relative contribution of galaxy starlight and AGN to these systems remains uncertain, especially for the galaxies with unusual blue+red spectral energy distributions. In this work, we use Balmer decrements to measure the independent dust attenuation of the broad and narrow emission-line components of a sample of 29 broad-line AGN identified from three public JWST spectroscopy surveys: CEERS, JADES, and RUBIES. Stacking the narrow components from the spectra of 25 sources with broad H α and no broad H β results in a median narrow H α /H β = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (consistent with A v = 0) and broad H α /H β >8.85 ( A v > 3.63). The narrow and broad Balmer decrements imply little to no attenuation of the narrow emission lines, which are consistent with being powered by star formation and located on larger physical scales. Meanwhile, the lower limit in the broad H α /H β decrement, with broad H β undetected in the stacked spectrum of 25 broad H α AGN, implies significant dust attenuation of the broad-line emitting region that is presumably associated with the central AGN. Our results indicate that these systems, on average, are consistent with heavily dust-attenuated AGN powering the red parts of their SED, while their blue UV emission is powered by unattenuated star formation in the host galaxy.

JWST Observations of Young protoStars (JOYS). Overview of program and early results

2025-06-17

E. F. van Dishoeck , Łukasz Tychoniec , W. R. M. Rocha +7 more | Astronomy and Astrophysics

The embedded phase of star formation is a crucial period in the development of a young star when the system still accretes matter, emerges from its natal cloud with assistance … The embedded phase of star formation is a crucial period in the development of a young star when the system still accretes matter, emerges from its natal cloud with assistance from powerful jets and outflows, and forms a disk, thus setting the stage for the birth of a planetary system. The mid-infrared spectral line observations now possible with unprecedented sensitivity, spectral resolution, and sharpness from the James Webb Space Telescope (JWST) are key for probing many of the physical and chemical processes on sub-arcsecond scales that occur in highly extincted regions. They provide unique diagnostics and complement millimeter observations. The aim of the JWST Observations of Young protoStars (JOYS) program is to address a wide variety of topics ranging from protostellar accretion and the nature of primeval jets, winds, and outflows to the chemistry of gas and ice in hot cores and cold dense protostellar environments to the characteristics of the embedded disks. We introduce the JOYS program and show representative results. The JWST Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) Integral Field Unit (IFU) 5--28 μm maps of 17 low-mass targets (23 if binary components are counted individually) and six high-mass protostellar sources were taken with resolving powers R=λ/Δ λ=1500-4000. We used small mosaics ranging from $1 1$ to $3 MRS tiles to cover ∼ 4'' to $20''$ fields of view providing spectral imaging on spatial scales down to ∼30 au (low mass) and ∼600 au (high mass). For HH 211, the complete ∼ 1' blue outflow lobe was mapped with the MRS. Atomic lines were interpreted with published shock models, whereas molecular lines were analyzed with simple rotation diagrams and local thermodynamic equilibrium slab models. We stress the importance of taking infrared pumping into account. Inferred abundance ratios were compared with detailed hot core chemical models including X-rays, whereas ice spectra were fit through comparison with laboratory spectra. The JWST MIRI-MRS spectra show a wide variety of features, with their spatial distribution providing key insight into their physical origin. The atomic line maps differ among refractory (e.g., Fe), semi-refractory (e.g., S), and volatile elements (e.g., Ne) and are linked to their different levels of depletion and local (shock) conditions. Jets are prominently seen in lines of Fe II and other refractory elements, whereas the pure rotational H_2 lines probe hot (∼ 1000 K) and warm (fewtimes 10^2 K) gas inside the cavity, as well as gas associated with jets, entrained outflows, and cavity walls for both low- and high-mass sources. Wide-angle winds are found in low-J H_2 lines. Nested stratified jet structures containing an inner ionized core with an outer molecular layer are commonly seen in the youngest sources. While S I follows the jet as seen in Fe II in the youngest protostars, it is different in more evolved sources, where it is concentrated on source. Noble gas lines such as Ne II 12.8 μm reveal a mix of jet shock and photoionized emission. The H I recombination lines serve as a measure of protostellar accretion rates but are also associated with more extended jets. Gaseous molecular emission (CO_2, C_2H_2, HCN, H_2O, CH_4, SO_2, SiO) is seen toward several sources, but it is cool compared with what is found in more evolved disks, with excitation temperatures of only 100--250 K, and likely associated with the warm inner envelopes (``hot cores'') . Along the outflow, CO_2 is often extended, thus contrasting with C_2H_2, which is usually centered on source. Water emission is commonly detected on source, even if relatively weak. Off source, it is seen only in the highest density shocks, such as those associated with NGC 1333 IRAS4B. Some sources show gaseous molecular lines in absorption, including NH_3 in one case. Deep ice features are seen toward the protostars, revealing not just the major ice components but also ions (as part of salts) and complex organic molecules, with comparable abundances from low- to high-mass sources. The relative abundances of some gas and ice species are similar, which is consistent with ice sublimation in hot cores. We present a second detection of HDO ice in a solar-mass source, with an HDO/H_2O ice ratio of ∼0.4%, thus providing a link with HDO/H_2O in disks and comets. A deep search for solid O_2 suggests that it is not a significant oxygen reservoir. Only a few embedded Class I disks show the same forest of water lines as Class II disks. This may be due to significant dust extinction of the upper layers in young disks caused by less settling of small dust as well as radial drift bringing in fresh dust. This paper illustrates the wide range of science questions that a single MIRI-MRS IFU data set can address. Our data suggest many similarities between low- and high-mass sources. Large source samples across evolutionary stages and luminosities are needed to further develop these diagnostics of the physics and chemistry of protostellar systems.

Temporal Changes in High-velocity Gas Associated with the Monoceros Loop SNR

2025-06-16

Adam M. Ritchey , S. R. Federman , N. Kameswara Rao +2 more | Research Notes of the AAS

Abstract We present observations of interstellar Na i and Ca ii absorption lines toward HD 47240, which probes shocked gas in the Monoceros Loop supernova remnant. The observations were obtained … Abstract We present observations of interstellar Na i and Ca ii absorption lines toward HD 47240, which probes shocked gas in the Monoceros Loop supernova remnant. The observations were obtained at five different epochs spanning the time period from 2017 January to 2024 September. Time variable Na i and Ca ii absorption is observed in two high-velocity components at +63 and +73 km s −1 . These are the same high-velocity features discussed by C. Dirks & D. M. Meyer, who found significant variations in Na i column densities between 2006 January and 2014 January. We discuss our new observations of temporal variability in the context of these and other previous observations of the high-velocity gas toward HD 47240. We speculate that the column density variations are a result of small-scale structure in the post-shock flow passing in front of the background star.

Observational Signatures of Disk Winds in Protoplanetary Disks: Differentiating Magnetized and Photoevaporative Outflows with Fully Coupled Thermochemistry

2025-06-16

Xiao Hu , Jaehan Bae , Zhaohuan Zhu +1 more | The Astrophysical Journal

Abstract Magnetized winds and photoevaporative winds are critical in shaping protoplanetary disk evolution. Using 2D axisymmetric (magneto)hydrodynamic simulations with fully coupled thermochemistry, we investigate the signatures of the two winds … Abstract Magnetized winds and photoevaporative winds are critical in shaping protoplanetary disk evolution. Using 2D axisymmetric (magneto)hydrodynamic simulations with fully coupled thermochemistry, we investigate the signatures of the two winds in CO and [C I ] Atacama Large Millimeter/submillimeter Array (ALMA) observations, and examine the potential to distinguish the origins. Our simulations reveal fundamental differences between the two winds: magnetized winds are colder and denser, exhibiting super-Keplerian rotation with small poloidal velocities of ≲1 km s −1 in the atmosphere ( z / R ≳ 0.45), while photoevaporative winds are hotter and less dense, exhibiting sub-Keplerian rotation with higher poloidal velocities of several kilometers per second. In addition to previously identified factors like thermal pressure gradient and disk’s self-gravity, we demonstrate that magnetic force and advection significantly influence rotational velocities of the gas in the wind, which lead to emission patterns that are distinct from Keplerian rotation in synthetic ALMA observations. Magnetized winds are visible in CO channel maps when wind loss rates are ≳10 −8 M ⊙ yr −1 . When wind loss rates are lower, magnetized winds produce subtle perturbations that resemble those produced by protoplanets. While strong X-ray and ultraviolet radiation photodissociates CO in photoevaporative winds, they can create observable ring-like substructures at disk surfaces. [C I ] emission is optically thin and could be most effective at detecting both winds in disks with high gas mass and/or high [C I ] abundance. Due to the spatially extended nature of the winds, using a large beam ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>≃</mml:mo> <mml:mn>0</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>″</mml:mi> </mml:mrow> </mml:mover> <mml:mn>4</mml:mn> </mml:math> for disks in nearby star-forming regions) will be helpful regardless of the tracer used.

The life cycle of giant molecular clouds in simulated Milky Way-mass galaxies

2025-06-16

Yang Ni , Hui Li , Mark Vogelsberger +3 more | Astronomy and Astrophysics

Giant molecular clouds (GMCs) are the primary sites of star formation in galaxies. Their evolution, driven by the interplay of gravitational collapse, stellar feedback, and galactic dynamics, is key to … Giant molecular clouds (GMCs) are the primary sites of star formation in galaxies. Their evolution, driven by the interplay of gravitational collapse, stellar feedback, and galactic dynamics, is key to understanding local star formation on GMC scales. However, tracking the full life cycle of GMCs across diverse galactic environments remains challenging and requires high-resolution hydrodynamical simulations and robust post-processing analysis. We aim to trace the complete life cycle of individual GMCs in high-resolution Milky Way–mass galaxy simulations to determine how different stellar feedback mechanisms and galactic-scale processes govern cloud lifetimes, mass evolution, and local star formation efficiency (SFE). We identified GMCs in simulated galaxies and tracked their evolution using cloud evolution trees. Via cloud evolution trees, we quantified the lifetimes and SFE of GMCs. We further applied our diagnostics to a suite of simulations with varying star formation and stellar feedback subgrid models and explored their impact together with galactic environments to the GMC life cycles. Our analysis reveals that GMCs undergo dynamic evolution, characterized by continuous gas accretion, gravitational collapse, and star formation, followed by disruption due to stellar feedback. The accretion process sustains the gas content throughout most of the GMC life cycles, resulting in a positive correlation between GMC lifetimes and their maximum masses. The GMC lifetimes range from a few to several tens of million years, with two distinct dynamical modes: (1) GMCs near the galactic center experience strong tidal disturbances, prolonging their lifetimes when they remain marginally unbound; (2) those in the outer regions are less affected by tides, remain gravitationally bound, and evolve more rapidly. In all model variations, we observe that GMC-scale SFE correlates with the baryonic surface density of GMCs, consistent with previous studies of isolated GMCs. Additionally, we emphasize the critical role of galactic shear in regulating GMC-scale star formation and refine the correlation between local SFE and surface density by including its effects. These findings demonstrate how stellar feedback and galactic-scale dynamics jointly shape GMC-scale star formation in realistic galactic environments.

Origin of the Shell Structure in the Primary Outflow from IRAS 15398−3359

2025-06-16

Tomoyuki Hanawa , Yuki Okoda , Yao-Lun Yang +1 more | The Astrophysical Journal

Abstract IRAS 15398−3359, a Class 0 protostar in the Lupus I star-forming region, is associated with three generations of outflows. The primary outflow, i.e., the most recent one, shows an … Abstract IRAS 15398−3359, a Class 0 protostar in the Lupus I star-forming region, is associated with three generations of outflows. The primary outflow, i.e., the most recent one, shows an internal structure named the “shell structure” in the near-infrared emission map. The shell structure is also seen in the emission lines of CO, H 2 CO, and other species. We find a similar structure in an underexpanded jet produced in aerodynamics and other engineering applications. A high-pressure gas ejected through a nozzle expands to form a supersonic flow. When the pressure of the ejected gas becomes lower than that of the ambient gas, the jet is compressed to form a shock wave. The shock-heated gas expands again to form substructures along the jet. We examine the similarity between the primary outflow of IRAS 15398−3359 and the industrial underexpanded jet and the possibility that the shell structure of the former is due to repeated expansion and compression in the direction perpendicular to the jet propagation.

Equivalent Width of the Interstellar Na <scp>i</scp> D1 and D2 Absorption Lines for Stars with E(B − V) < 0.15

2025-06-16

P. F. L. Maxted | Research Notes of the AAS

Abstract New measurements of the equivalent width of the interstellar Na i D 1 and D 2 absorption lines for 62 bright B-type stars with E ( B − V … Abstract New measurements of the equivalent width of the interstellar Na i D 1 and D 2 absorption lines for 62 bright B-type stars with E ( B − V ) < 0.15 are used to recalibrate the relation between these quantities in this low-reddening regime, and to quantify the scatter around this relation. Stars showing multiple components in their interstellar Na i lines clearly show a larger total equivalent width at the same E ( B − V ) than stars with a single interstellar Na i absorption lines. Semi-empirical relations are derived that allow for the reddening toward stars showing single interstellar Na i absorption lines to be estimated. Previous calibrations of this relation are typically found to underestimate E ( B − V ) for these stars.

HDO Ice Detected toward an Isolated Low-mass Protostar with JWST

2025-06-16

K. Slavicinska , Łukasz Tychoniec , María Gabriela Navarro +7 more | The Astrophysical Journal Letters

Abstract Water is detected in environments representing every stage of star and solar system formation, but its chemical evolution throughout these stages remains poorly constrained. Deuterium ratios offer a means … Abstract Water is detected in environments representing every stage of star and solar system formation, but its chemical evolution throughout these stages remains poorly constrained. Deuterium ratios offer a means of probing chemical links between water in different cosmic regions because of their sensitivity to physicochemical conditions. Here, we present the first detection of the 4.1 μ m HDO ice feature with JWST toward a low-mass protostar, L1527 IRS, which may eventually grow to a Sun-like mass. We measure an ice HDO/H 2 O ratio of 4.4 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mi>-1.7</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>+3.7</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> × 10 −3 , where the reported error is dominated by uncertainties in continuum definition and ice band strengths. This fraction is similar to the gas HDO/H 2 O ratios measured in the warm (>100 K) inner cores of other low-mass protostellar envelopes and protoplanetary disks found in comparably isolated star-forming regions. Such a similarity tentatively supports the assumption that water vapor detected in these regions is not significantly altered by gas-phase reactions following ice sublimation. It also supports the hypothesis that pre- and protostellar water ice is largely inherited in a chemically unaltered state by outer protoplanetary disks. However, the fraction is a factor of ∼4–10 times higher than the gas HDO/H 2 O ratios measured toward comets and low-mass protostars in clustered star-forming regions. This difference may be due to either gas-phase water reprocessing in protostellar envelopes and protoplanetary disks or differences between prestellar conditions of isolated dense cores and the clustered star-forming regions that are more analogous to the environment in which our Sun formed.

Study of the Structure of Interstellar Medium Towards the Star 62 Tau With <scp>ESPRESSO</scp> Spectrograph

2025-06-15

A. Bondar , J. Krełowski | Astronomische Nachrichten

ABSTRACT We have conducted investigations of the structure of interstellar medium towards the star 62 Tau using a very high resolving power ( R = 170 000) spectrum of ESPRESSO … ABSTRACT We have conducted investigations of the structure of interstellar medium towards the star 62 Tau using a very high resolving power ( R = 170 000) spectrum of ESPRESSO spectrograph. Basic goals of this work are as follows: to search for radial velocity components in the interstellar spectral lines, detectable in the star's spectrum; to measure heliocentric radial velocities ( V r ) of the intervening interstellar clouds, to determine Doppler parameter b and the column densities (N) of the atoms and molecules present in the clouds. Using a profile fit procedure we found the components of the atomic and molecular lines with the V r between 11–18.5 km s. Only two main radial velocity components for every spectral feature could be discerned confidently. Thus, it was found that the interstellar matter on this sightline is mostly concentrated in the interstellar clouds with V r 15 and 18 km s. The column densities, yielded with the profile fits are in a good agreement with those found earlier by other researchers. The profiles of the interstellar molecular lines (CN, CH and CH) in the star's spectrum were analysed for the first time with such a high resolution.

Magnetic reconnection as the driving factor behind high-mass protostellar luminosity flares

2025-06-12

Xi Chen , Junting Liu , O. S. Bayandina +7 more | Communications Physics

Truncated Star Formation and Ram Pressure Stripping in the Coma Cluster

2025-06-12

Ariel O. Broderick , Ian Roberts , Michael J. Hudson | The Astrophysical Journal

Abstract We use 45 galaxies from the Mapping Nearby Galaxies at Apache Point Observatory survey to study the physical drivers of star formation quenching in the Coma Cluster. We measure … Abstract We use 45 galaxies from the Mapping Nearby Galaxies at Apache Point Observatory survey to study the physical drivers of star formation quenching in the Coma Cluster. We measure specific star formation rate (sSFR) radial profiles for the Coma sample as well as a control sample of noncluster field galaxies. We find that compared to the control sample, galaxies within the Coma Cluster have sSFR profiles that fall off more steeply with galactocentric radius. We then apply a toy model based on slow-then-rapid quenching via ram pressure stripping. We find that this model is able to reproduce the difference in sSFR profiles between field and Coma galaxies. These results demonstrate that ram pressure stripping plays a significant role in quenching star formation in the nearest massive galaxy cluster.

Determining the Methanol Deuteration in the Disk Around V883 Orionis with Laboratory Measured Spectroscopy

2025-06-12

Shaoshan Zeng , Jae-Hong Jeong , Takahiro Oyama +3 more | The Astronomical Journal

Abstract Deuterium fractionation, as studied through mono-deuterated methanol, is frequently used as a diagnostic tool to trace the physical conditions and chemical evolution of interstellar sources. This study investigates methanol … Abstract Deuterium fractionation, as studied through mono-deuterated methanol, is frequently used as a diagnostic tool to trace the physical conditions and chemical evolution of interstellar sources. This study investigates methanol deuteration in the disk around V883 Ori, utilising recent laboratory spectroscopic data for CH 2 DOH and CH 3 OD along with Atacama Large Millimeter/submillimeter Array observations. The derived column densities for CH 2 DOH and CH 3 OD are (5.14 ± 0.08) × 10 16 cm −2 and (4.22 ± 0.06) × 10 16 cm −2 , respectively. The analysis demonstrates the influence of spectroscopic data on determining molecular column density, excitation temperature, and, most importantly, the inferred D/H ratio. The D/H ratio for CH 2 DOH is calculated to be (7.3 ± 1.5) × 10 −3 after applying a statistical correction, while the D/H ratio for CH 3 OD is (1.79 ± 0.36) × 10 −2 . The discovery of an unexpectedly low CH 2 DOH/CH 3 OD ratio (1.22 ± 0.02) in V883 Ori, however, raises further questions about the synthesis and chemical processes involved in CH 3 OD formation. Overall, this study underscores the importance of accurate spectroscopic data for studies of isotopic fractionation and provides new insights into methanol deuteration chemistry in star-forming regions. Future research, combining updated spectroscopy and chemical modeling, will help further constrain these processes across different masses and evolutionary stages.

NO and c-C3H2 in the Outer Galaxy: High Molecular Abundances at R GC > 13 kpc

2025-06-11

Lilia Koelemay , L. M. Ziurys | The Astrophysical Journal

Abstract Observations of the J Ka, Kc = 4 1,4 → 3 0,3 , 4 0,4 → 3 1,3 , and 2 2,0 → 1 1,1 rotational lines of c-C … Abstract Observations of the J Ka, Kc = 4 1,4 → 3 0,3 , 4 0,4 → 3 1,3 , and 2 2,0 → 1 1,1 rotational lines of c-C 3 H 2 and the J = 3/2 → 1/2, Ω = 1/2 transition of NO (X 2 Π r ) were conducted at 2 mm toward 20 Galactic edge clouds with R GC = 10.8–23.5 kpc using the Arizona Radio Observatory 12 m telescope. The c-C 3 H 2 molecule was detected in all 20 objects in the sample, based typically on 2–3 transitions. NO, which exhibits a distinct pattern of lambda doubling and hyperfine splitting in the measured line, was identified in 16 clouds, with distances as far as R GC ∼ 23.5 kpc. While a 3 mm transition of c-C 3 H 2 had been observed before in some of the sample clouds, NO had not previously been detected at such large distances from the Galactic center. These new identifications double the number of molecular clouds known to contain NO. From a radiative transfer analysis, fractional abundances, relative to H 2 , were determined to be f (c-C 3 H 2 ) ∼ 0.5–39.8 × 10 −10 and f (NO) ∼ 0.2–21.2 × 10 −8 . These abundances are comparable to values observed in molecular clouds in the inner Galaxy (R GC < 12 kpc). The abundances therefore appear to remain relatively constant with increasing galactocentric distance. These results suggest that elemental abundance gradients at R GC ≥ 15 kpc in C, N, and O are not as severe as predicted. They also indicate that gas-phase chemistry in the outer Galaxy is quite robust, strengthening the case for widening the extent of the Galactic habitable zone.

Global Simulations of Gravitational Instability in Protostellar Disks with Full Radiation Transport. I. Stochastic Fragmentation with Optical-depth-dependent Rate and Universal Fragment Mass

2025-06-10

Wenrui Xu , Yan-Fei Jiang , Matthew W. Kunz +1 more | The Astrophysical Journal

Abstract Fragmentation in a gravitationally unstable accretion disk can be an important pathway for forming stellar/planetary companions. To characterize quantitatively the condition for and outcome of fragmentation under realistic thermodynamics, … Abstract Fragmentation in a gravitationally unstable accretion disk can be an important pathway for forming stellar/planetary companions. To characterize quantitatively the condition for and outcome of fragmentation under realistic thermodynamics, we perform global 3D simulations of gravitationally unstable disks at various cooling rates and cooling types, including the first global simulations of gravitational instability that employ full radiation transport. We find that fragmentation is a stochastic process, with the fragment generation rate per disk area p frag showing an exponential dependence on the parameter β ≡ Ω K t cool , where Ω K is the Keplerian rotation frequency, and t cool is the average cooling timescale. Compared to a prescribed constant β , radiative cooling in the optically thin/thick regime makes p frag decrease slower/faster in β ; the critical β corresponding to ∼1 fragment per orbit is ≈3, 5, and 2 for constant β , optically thin, and optically thick cooling, respectively. The distribution function of the initial fragment mass is remarkably insensitive to disk thermodynamics. Regardless of cooling rate and optical depth, the typical initial fragment mass is m frag ≈ 40 M tot h 3 , with M tot being the total (star+disk) mass and h = H / R being the disk aspect ratio. Applying this result to typical Class 0/I protostellar disks, we find m frag ∼ 20 M J , suggesting that fragmentation more likely forms brown dwarfs. Given the finite width of the m frag distribution, forming massive planets is also possible.

Revealing A Major Merger in the Nearby Galaxy Group IC 1262 with Chandra Observations

2025-06-10

Yu Wang | Research in Astronomy and Astrophysics

Abstract We analyze the deep Chandra data of the nearby IC1262 group, and find that the bow-shaped structure, located about 17 kpc ($25^{\prime\prime}$) east of the X-ray peak, is a … Abstract We analyze the deep Chandra data of the nearby IC1262 group, and find that the bow-shaped structure, located about 17 kpc ($25^{\prime\prime}$) east of the X-ray peak, is a cold front moving eastward with a Mach number of M=0.7$\pm 0.1$. Furthermore, the line-of-sight velocity distribution of the member galaxies is clearly divided into two subgroups. Assuming the same mass-to light ratio, the group is undergoing a major merger. Since the cooler core of the group as a whole is not destroyed by the merger, and the high-velocity subgroup has a component of eastward movement, it can be naturally explained that the cold front appears on the east side of the group center.