LSD: Lyman-break galaxies Stellar populations and Dynamics - I. Mass, metallicity and gas at<i>z</i>∼ 3.1

Abstract

We present the first results of a project, LSD, aimed at obtaining\nspatially-resolved, near-infrared spectroscopy of a complete sample of\nLyman-Break Galaxies at z~3. Deep observations with adaptive optics resulted in\nthe detection of the main optical lines, such as [OII], Hbeta and [OIII], which\nare used to study sizes, SFRs, morphologies, gas-phase metallicities, gas\nfractions and effective yields. Optical, near-IR and Spitzer/IRAC photometry is\nused to measure stellar mass. We obtain that morphologies are usually complex,\nwith the presence of several peaks of emissions and companions that are not\ndetected in broad-band images. Typical metallicities are 10-50% solar, with a\nstrong evolution of the mass-metallicity relation from lower redshifts. Stellar\nmasses, gas fraction, and evolutionary stages vary significantly among the\ngalaxies, with less massive galaxies showing larger fractions of gas. In\ncontrast with observations in the local universe, effective yields decrease\nwith stellar mass and reach solar values at the low-mass end of the sample.\nThis effect can be reproduced by gas infall with rates of the order of the\nSFRs. Outflows are present but are not needed to explain the mass-metallicity\nrelation. We conclude that a large fraction of these galaxies are actively\ncreating stars after major episodes of gas infall or merging.\n