Metallicity evolution, metallicity gradients, and gas fractions at z ~ 3.4^⋆,⋆⋆

¹ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
e-mail: troncoso@astro.rub.de
² Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany
³ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
⁴ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁷ Dip. di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, 50019 Sesto F.no, Firenze, Italy
⁸ INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
⁹ Dipartimento di Fisica e Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁰ The Hakubi Center for Advanced Research, Kyoto University, 606-8302 Kyoto, Japan
¹¹ Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, 606-8502 Kyoto, Japan

Received: 18 June 2013
Accepted: 10 December 2013

Abstract

We used near-infrared integral field spectroscopic observations from the AMAZE and LSD ESO programs to constrain the metallicity in a sample of 40 star-forming galaxies at 3 < z < 5 (most of which are at z ~ 3.4). We measured metallicities by exploiting strong emission-line diagnostics. We found that a significant fraction of star-forming galaxies at z ~ 3.4 deviate from the fundamental metallicity relation (FMR), with a metallicity of up to a factor of ten lower than expected according to the FMR. This deviation does not correlate with the dynamical properties of the galaxy or with the presence of interactions. To investigate the origin of the metallicity deviation in more detail, we also inferred information on the gas content by inverting the Schmidt-Kennicutt relation, assuming that the latter does not evolve out to z ~ 3.4. In agreement with recent CO observational data, we found that in contrast with the steeply rising trend at 0 < z < 2, the gas fraction in massive galaxies remains constant, with an indication of a marginal decline at 2 < z < 3.5. When combined with the metallicity information, we infer that to explain the low metallicity and gas content in z ~ 3.4 galaxies, both prominent outflows and massive pristine gas inflows are needed. In ten galaxies we can also spatially resolve the metallicity distribution. We found that the metallicity generally anticorrelates with the distribution of star formation and with the gas surface density. We discuss these findings in terms of pristine gas inflows toward the center, and outflows of metal-rich gas from the center toward the external regions.