The Mass-Metallicity and Luminosity-Metallicity Relation from DEEP2 at z ~ 0.8

TL;DR

This study measures the evolution of the mass-metallicity and luminosity-metallicity relations at z ~ 0.8, revealing that massive galaxies reach local chemical enrichment levels while lower mass galaxies lag behind, supporting the cosmic downsizing scenario.

Contribution

It provides a large, consistent dataset of metallicities at z ~ 0.8 and compares it with local relations, highlighting mass-dependent evolution in galaxy chemical properties.

Findings

High-mass galaxies at z ~ 0.8 have similar metallicities to local galaxies.

Lower-mass galaxies at z ~ 0.8 have lower metallicities than local counterparts.

The B-band luminosity evolution is mass-dependent and not a reliable proxy for stellar mass.

Abstract

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 (DEEP2) 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 (log(M/M_solar)~10.6) at z ~ 0.8 have attained the chemical enrichment seen in the local universe, while lower stellar mass galaxies (log(M/M_solar)~9.2) at z ~ 0.8 have lower metallicities (Delta log(O/H)~0.15 dex) 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.