We examine the redshift evolution of standard strong emission-line diagnostics for Hbeta-selected star-forming galaxies using the local SDSS sample and a new z = 0.2 - 2.3 sample obtained from HST WFC3 grism and Keck DEIMOS and MOSFIRE data. We use the SDSS galaxies to show that there is a systematic dependence of the strong emission-line properties on Balmer-line luminosity, which we interpret as showing that both the N/O abundance and the ionization parameter increase with increasing line luminosity. Allowing for the luminosity dependence tightens the diagnostic diagrams and the metallicity calibrations. The combined SDSS and high-redshift samples show that there is no redshift evolution in the line properties once the luminosity correction is applied, i.e., all galaxies with a given L(Hbeta) have similar strong emission-line distributions at all the observed redshifts. We argue that the best metal diagnostic for the high-redshift galaxies may be a luminosity-adjusted version of the [NII]6584/Halpha metallicity relation.
@article{arxiv.1512.00017,
title = {Luminosity Dependence and Redshift Evolution of Strong Emission-line Diagnostics in Star-Forming Galaxies},
author = {Lennox L. Cowie and Amy J. Barger and Antoinette Songaila},
journal= {arXiv preprint arXiv:1512.00017},
year = {2016}
}
Comments
Accepted for publication in ApJ. 16 pages, 15 figures