IMAGES IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies from z ∼ 0.8

Astronomy and Astrophysics (Impact Factor: 4.38). 12/2008; 492(2). DOI: 10.1051/0004-6361:200810435
Source: arXiv


Context. Intermediate mass galaxies (> 10$^{10}$ $M_\odot$) 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 in the last 6 to 8 Gyr, and likely already have formed a significant fraction of their stellar mass, often showing perturbed morphologies and kinematics.Aims. We have gathered a representative sample of 88 such galaxies and have provided robust estimates of their gas phase metallicity.Methods. We used moderate spectral resolution spectroscopy at VLT/FORS2 with an unprecedentedly high $S/N$ allowing us to remove biases coming from interstellar absorption lines and extinction, to establish robust values of $R_{23}$ = ([OII]$\lambda$3727 + [OIII]$\lambda\lambda$4959, 5007)/H$\beta$.Results. 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 evolves 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 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 closed 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.Conclusions. Our study further supports the rapid evolution of $z$ ~ 0.4–1 galaxies. Gas exchange between galaxies is likely the main cause of this evolution.

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