The stellar population of metal-poor galaxies at z ≈ 0.8 and the evolution of the mass-metallicity relation

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-* approximate to 10(8.1)-10(9.5) M-circle dot. Combined with the Balmer-derived star formation rates (SFRs), these galaxies have average inverse SFR/M-* of approximate to 100 Myr. The evolution of stellar mass-gas metallicity relation to z approximate to 0.8 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)(-1.45-0.76+0.61 .) We find that the shape of the z approximate to 0.8 mass-metallicity relation, a steep rise in metallicity at low stellar masses, transitioning to a plateau at higher masses, is consistent with z similar to 0.1 studies. We also compare the evolution in metallicity between z approximate to 0.8 and z similar to 0.1 against recent strong-line diagnostic studies at intermediate redshifts and find good agreement. Specifically, we find that lower mass galaxies (4 x 10(8) M-circle dot) built up their metal content 1.6 times more rapidly than higher mass galaxies (10(10) M-circle dot). 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 approximate to 0.8 low-mass galaxies.