Images IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies since z=0.8

TL;DR

This study shows that the gas-phase oxygen abundance in intermediate mass galaxies has evolved significantly since z=0.8, driven mainly by gas infall and interactions, with implications for galaxy formation and evolution.

Contribution

It provides robust measurements of metallicity evolution in intermediate mass galaxies at z~0.6 using high-quality spectroscopy, confirming rapid chemical evolution and the role of external gas supply.

Findings

Galaxies at z~0.6 are twice less metal-rich than local counterparts.

Gas-phase metallicity evolves linearly from z=1 to 0.

Approximately 30% of local stellar mass formed via external gas accretion.

Abstract

Intermediate mass galaxies (logM(Msun)>10) at z~0.6 are the likeliest progenitors of the present-day numerous population of spirals. There is growing evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and likely have formed a significant fraction of their stellar mass, often showing perturbed morphologies and kinematics. We have gathered a representative sample of 88 such galaxies and have provided robust estimates of their gas phase metallicity. For doing so, we have used moderate spectral resolution spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases coming from interstellar absorption lines and extinction to establish robust values of R23=([OII]3727 + [OIII]4959,5007)/Hbeta. We definitively confirm that the predominant population of z~0.6 starbursts and luminous IR galaxies (LIRGs) are on average, two times less metal rich than the local galaxies at a given stellar mass. We do find that the metal abundance of the gaseous phase of galaxies is evolving linearly with time, from z=1 to z=0 and after comparing with other studies, from z=3 to z=0. Combining our results with the reported evolution of the Tully Fisher relation, we do find that such an evolution requires that ~30% of the stellar mass of local galaxies have been formed through an external supply of gas, thus excluding the close box model. Distant starbursts & LIRGs have properties (metal abundance, star formation efficiency & morphologies) similar to those of local LIRGs. Their underlying physics is likely dominated by gas infall probably through merging or interactions. Our study further supports the rapid evolution of z~0.4-1 galaxies. Gas exchanges between galaxies is likely the main cause of this evolution.