New light on the search for low-metallicity galaxies — I. The N2 calibrator
New light on the search for low-metallicity galaxies — I. The N2 calibrator
We present a simple metallicity estimator based on the logarithmic [N ii] λ6584/Hα ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in a metallicity sequence from redshift survey-quality data even for moderately low spectral resolution.