IMAGES IV: strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies from z ~ 0.8^*

¹ GEPI , Observatoire de Paris, CNRS, University Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France e-mail: myriam.rodrigues@obspm.fr
² CENTRA, Instituto Superior Tecnico, Av. Rovisco Pais 1049-001 Lisboa, Portugal
³ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁴ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China
⁵ Laboratoire d'Astrophysique de Marseille, Observatoire Astronomique de Marseille-Provence, 2 place Le Verrier, 13248 Marseille, France
⁶ MPIA, Königstuhl 17, 69117 Heidelberg, Germany
⁷ IFARHU-SENACYT, Technological University of Panama, 0819-07289 Panama, Rep. of Panama
⁸ Centre de Recherche Astronomique de Lyon, 9 Avenue Charles André, 69561 Saint-Genis-Laval Cedex, France
⁹ Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007, India
¹⁰ Stockholm Observatory, AlbaNova University Center, Stockholms Center for Physics, Astronomy and Biotechnology, Roslagstullsbacken 21, 10691 Stockholm, Sweden
¹¹ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹² Department of Physics, University of Calicut, Kerala 673635, India
¹³ INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Florence, Italy
¹⁴ IASF-INAF - via Bassini 15, 20133 Milano, Italy

Received: 20 June 2008
Accepted: 21 September 2008

Abstract

Context. Intermediate mass galaxies (> 10¹⁰ ) 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  allowing us to remove biases coming from interstellar absorption lines and extinction, to establish robust values of R₂₃ = ([OII]λ3727 + [OIII]4959, 5007)/Hβ.

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 to and after comparing with other studies, from to . 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.