K-band Imaging of strong CaII-absorber host galaxies at z~1

TL;DR

This study uses K-band imaging to analyze the environments of strong CaII absorption systems at z~1, revealing a significant excess of luminous galaxies nearby and suggesting a luminosity-dependent cross-section for CaII absorption.

Contribution

It provides the first detailed analysis of the galaxy environments of CaII absorbers at z~1, introducing a luminosity-dependent model for CaII absorption cross-section.

Findings

Significant excess of luminous galaxies within 50kpc of CaII absorbers.

Luminosity-dependent cross-section for CaII absorption is stronger than for MgII.

Large physical separations imply a low filling factor (~10%) for CaII-absorbing gas.

Abstract

We present K-band imaging of fields around 30 strong CaII absorption line systems, at 0.7<z<1.1, three of which are confirmed Damped Lyman-alpha systems. A significant excess of galaxies is found within 6"0 (~50kpc) from the absorber line-of-sight. The excess galaxies are preferentially luminous compared to the population of field galaxies. A model in which field galaxies possess a luminosity-dependent cross-section for CaII absorption of the form (L/L*)^0.7 reproduces the observations well. The luminosity-dependent cross-section for the CaII absorbers appears to be significantly stronger than the established (L/L*)^0.4 dependence for MgII absorbers. The associated galaxies lie at large physical distances from the CaII-absorbing gas; we find a mean impact parameter of 24kpc (H0=70km\s\Mpc). Combined with the observed number density of CaII absorbers the large physical separations result in an inferred filling factor of only ~10 per cent. The physical origin of the strong CaII absorption remains unclear, possible explanations vary from very extended disks of the luminous galaxies to associated dwarf galaxy neighbours, remnants of outflows from the luminous galaxies, or tidal debris from cannibalism of smaller galaxies.