A monolithic collapse origin for the thin and thick disc structure of the S0 galaxy ESO 243-49^⋆

¹ University of Oulu, Astronomy Research Unit, PO Box 3000, 90014 Oulu, Finland
e-mail: seb.comeron@gmail.com
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Received: 11 July 2016
Accepted: 13 August 2016

Abstract

ESO 243-49 is a high-mass (circular velocity v_c ≈ 200 km s^-1), edge-on S0 galaxy in the Abell 2877 cluster at a distance of ~95 Mpc. To elucidate the origin of the thick disc of this S0 galaxy, we use Multi Unit Spectroscopic Explorer (MUSE) science verification data to study its kinematics and stellar populations. The thick disc emits ~80% of the light at heights in excess of (1.6 kpc). The rotation velocities of its stars lag by 30−40 km s^-1 compared to those in the thin disc, which is compatible with the asymmetric drift. The thick disc is found to be more metal-poor than the thin disc, but both discs have old ages. We suggest an internal origin for the thick disc stars in high-mass galaxies. We propose that the thick disc formed either a) first in a turbulent phase with a high star formation rate and that a thin disc formed shortly afterwards, or b) because of the dynamical heating of a thin pre-existing component. Either way, the star formation in ESO 243-49 was quenched just a few Gyr after the galaxy was born and the formation of a thin and a thick disc must have occurred before the galaxy stopped forming stars. The formation of the discs was so fast that it could be described as a monolithic collapse where several generations of stars formed in rapid succession.