Formation of galactic disks through gas-rich mergers

Abstract

To probe the progenitors of the numerous massive spirals requires to dissect distant galaxy properties through spatially-resolved kinematics, detailed morphologies and photometry from UV to mid-IR. So far IMAGES is the only representative sample studied that way. Six billion years ago, 50% of spiral progenitors were experiencing major mergers, evidenced by the combination of their peculiar kinematics and morphology. IMAGES provides the observational point of the spiral rebuilding scenario, which agrees with predictions from the LCDM. It reconciles the disk formation or survival with the observed merger rate and allows to reproduce realistic galactic disks with sufficient angular momentum. Several consequences are expected in the Local Universe, because ancient major mergers had let imprints in galaxy haloes, including the most spectacular cases of NGC5907 and M31. An ancient merger in the later galaxy may have left many debris within the Local Group.