The Stellar Population of Metal-Poor Galaxies at z $\approx$ 0.8 and the Evolution of the Mass-Metallicity Relation

Abstract

We present results from deep Spitzer/Infrared Array Camera (IRAC) observations of 28 metal-poor, strongly star-forming galaxies selected from the DEEP2 Galaxy Survey. By modelling infrared and optical photometry, we derive stellar masses and other stellar properties. We determine that these metal-poor galaxies have low stellar masses, $M_{\star}$ $\approx10^{8.1}$-$10^{9.5}$ $M_{\odot}$. Combined with the Balmer-derived star formation rates (SFRs), these galaxies have average inverse SFR/$M_{\star}$ of $\approx$100 Myr. The evolution of stellar mass-gas metallicity relation to $z\approx0.8$ is measured by combining the modelled masses with previously obtained spectroscopic measurements of metallicity from [O III] $\lambda$4363 detections. Here, we include measurements for 79 galaxies from the Metal Abundances across Cosmic Time Survey. Our mass-metallicity relation is lower at a given stellar mass than at $z=0.1$ by 0.27 dex. This demonstrates a strong evolution in the mass-metallicity relation, $(1+z)^{-1.45^{+0.61}_{-0.76}}$. We find that the shape of the $z\approx0.8$ mass-metallicity relation, a steep rise in metallicity at low stellar masses, transitioning to a plateau at higher masses, is consistent with $z\sim0.1$ studies. We also compare the evolution in metallicity between $z\approx0.8$ and $z\sim0.1$ against recent strong-line diagnostic studies at intermediate redshifts and find good agreement. Specifically, we find that lower mass galaxies ($4\times10^8$ $M_{\odot}$) built up their metal content 1.6 times more rapidly than higher mass galaxies ($10^{10}$ $M_{\odot}$). Finally, we examine whether the mass-metallicity relation has a secondary dependence on SFR, and statistically concluded that there is no strong secondary dependence for $z\approx0.8$ low-mass galaxies.