The mass-metallicity and luminosity-metallicity relations from deep2 at z ∼ 0.8

We present the mass-metallicity (MZ) and luminosity-metallicity (LZ) relations at z 0.8 from 1350 galaxies in the Deep Extragalactic Evolutionary Probe 2 survey. We determine stellar masses by fitting the spectral energy distribution inferred from photometry with current stellar population synthesis models. This work raises the number of galaxies with metallicities at z 0.8 by more than an order of magnitude. We investigate the evolution in the MZ and LZ relations in comparison with local MZ and LZ relations determined in a consistent manner using 21, 000 galaxies in the Sloan Digital Sky Survey. We show that high stellar mass galaxies (M 10^10.6 M) at z 0.8 have attained the chemical enrichment seen in the local universe, while lower stellar mass galaxies (M 10^9.2 M) at z 0.8 have lower metallicities (Δlog(O/H) 0.15dex) than galaxies at the same stellar mass in the local universe. We find that the LZ relation evolves in both metallicity and B-band luminosity between z 0.8 and z 0, with the B-band luminosity evolving as a function of stellar mass. We emphasize that the B-band luminosity should not be used as a proxy for stellar mass in chemical evolution studies of star-forming galaxies. Our study shows that both the metallicity evolution and the B-band luminosity evolution for emission-line galaxies between the epochs are a function of stellar mass, consistent with the cosmic downsizing scenario of galaxy evolution.