K-band imaging of strong Ca ii-absorber host galaxies at z ∼ 1

Abstract

We present K-band imaging of fields around 30 strong Ca ii absorption-line systems, at 0.7 < z < 1.2, three of which are confirmed damped Lyman α systems. A significant excess of galaxies is found within 6.0 arcsec (≃50 kpc) 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 Ca ii absorption of the form (L/L*)0.7 reproduces the observations well. The luminosity-dependent cross-section for the Ca ii absorbers appears to be significantly stronger than the established (L/L*)0.4 dependence for Mg ii absorbers. The associated galaxies lie at large physical distances from the Ca ii-absorbing gas; we find a mean impact parameter of 24 kpc (H0 = 70 km s-1 Mpc-1). Combined with the observed number density of Ca ii absorbers the large physical separations result in an inferred filling factor of only ∼10 per cent. The physical origin of the strong Ca ii absorption remains unclear, possible explanations vary from very extended discs of the luminous galaxies to associated dwarf galaxy neighbours, remnants of outflows from the luminous galaxies, or tidal debris from cannibalism of smaller galaxies. © 2007 RAS.