The Gemini Deep Deep Survey. VII. The redshift evolution of the mass-metallicity relation

We have investigated the mass-metallicity (M-Z) relation using galaxies at 0: 4 < z < 1.0 from the Gemini Deep Deep Survey (GDDS) and Canada-France Redshift Survey (CFRS). Deep K- and z'-band photometry allowed us to measure stellar masses for 69 galaxies. From a subsample of 56 galaxies, for which metallicity of the interstellar medium is also measured, we identified a strong correlation between mass and metallicity for the first time in the distant universe. This was possible because of the larger baseline spanned by the sample in terms of metallicity ( a factor of 7) and mass ( a factor of 400) than in previous works. This correlation is much stronger and tighter than the luminosity-metallicity relation, confirming that stellar mass is a more meaningful physical parameter than luminosity. We find clear evidence for temporal evolution in the M-Z relation in the sense that at a given mass, a galaxy at z similar to 0.7 tends to have lower metallicity than a local galaxy of similar mass. We use the z similar to 0.1 Sloan Digital Sky Survey M-Z relation and a small sample of z similar to 2.3 Lyman break galaxies with known mass and metallicity to propose an empirical redshift-dependent M-Z relation. According to this relation the stellar mass and metallicity in small galaxies evolve for a longer time than they do in massive galaxies. This relation predicts that the generally metal-poor damped Ly alpha galaxies have stellar masses of the order of 10(8.8) M-circle dot ( with a dispersion of 0.7 dex) all the way from z similar to 0.2 to 4. The observed redshift evolution of the M-Z relation can be reproduced remarkably well by a simple closed-box model in which the key assumption is an e-folding time for star formation that is higher or, in other words, a period of star formation that lasts longer in less massive galaxies than in more massive galaxies. Such a picture supports the downsizing scenario for galaxy formation.