A SEARCH FOR GALAXIES PRODUCING METAL-RICH QUASAR ABSORBERS

Abstract

We have carried out optical and near-IR imaging of three fields with metal-rich damped or sub-damped Lyα quasar absorption systems, using the Goddard Fabry-Perot system and the Near-IR Camera and Fabry-Perot Spectrometer at the Apache Point Observatory 3.5 m telescope. The aim of these observations was to detect the underlying galaxies and search for their redshifted [O II] λ3727 emission and optical/near-IR continuum. Candidate absorber galaxies separated by 25-88 from the quasars are detected in two of three absorber fields in the H and KS bands at >3σ level. The potentially high success rate in finding galaxy counterparts of metal-rich absorbers suggests that the metal-rich absorbers may be easier to detect in imaging observations than the metal-poor absorbers targeted in many previous imaging studies of damped Lyα absorbers. Of course, spectroscopic confirmation of the candidate galaxies is necessary to establish whether they are at the absorber redshifts. Interestingly, no significant [O II] emission is detected in any of the fields at >3σ level, implying limits on the star formation rate (SFR) of 0.7-2.6 M ☉ yr–1 per 076 × 076 region, if no dust extinction is assumed. The 3σ sensitivity levels in the narrowband images (tuned to the expected positions of the redshifted [O II] λ3727) ranged between 1.3 × 10–17 and 3.3 × 10–17 erg s–1 cm–2 in observed frame. If the candidate galaxies are at the absorber redshifts, the lack of [O II] emission would suggest that the metal-rich absorbers may arise in early-type or S0 galaxies that do not have significant current star formation. We compare our results with those compiled from the literature and with predictions of global average SFR based on the models of cosmic chemical evolution. Together, these studies indicate SFRs much lower than the predictions for the global mean SFR.