The host galaxies of strong Ca II quasar absorption systems at z 0.5

We present new imaging and spectroscopic observations of the fields of five quasars with very strong intervening Ca II absorption systems at redshifts z(abs) < 0.5 selected from the Sloan Digital Sky Survey. Recent studies of these very rare absorbers indicate that they may be related to damped Lyman alpha systems (DLAs). In all five cases, we identify a galaxy at the redshift of the Ca II system with impact parameters up to similar to 24 kpc. In four out of five cases the galaxies are luminous ( L similar or equal to L*), metal-rich ( Z similar or equal to Z(circle dot)), massive (velocity dispersion sigma similar or equal to 100 km s(-1)) spirals. Their star formation rates (SFRs), deduced from Ha emission, are high, in the range SFR = 0.3-30 M-circle dot yr(-1). In our analysis, we paid particular attention to correcting the observed emission-line fluxes for stellar absorption and dust extinction. We show that these effects are important for a correct SFR estimate; the difficulties of incorporating such corrections in previous low-z studies of DLA-selected galaxies has probably led to an underestimate of the star formation activity in at least some DLA hosts. We discuss possible links between Ca II-selected galaxies and DLAs and outline future observations which will help clarify the relationship between these different classes of quasar absorbers.