Emission Line Abundances of Absorption Selected Galaxies at z<0.5

Abstract

We have obtained optical spectra of four galaxies associated with MgII QSO absorbers at redshifts 0.10 < z < 0.45. We calculate the gas-phase oxygen abundance of these galaxies using the empirical R23 strong line method. The absolute B-band magnitudes of the galaxies span -20.6 < M_B < -18.3. If the metallicities lie on the R23 upper branch (8.4 < log (O/H) + 12 < 8.9), then the metallicities of these absorption selected galaxies span the range between 0.5--1.4 solar and would be consistent with the well-known luminosity-metallicity relation for 0.10 < z < 0.45 emission-line galaxies. However, such metallicities would be 0.5--1.0 dex higher than those observed in damped Lyman alpha systems (DLAs) via absorption line measurements at similar redshifts. Conversely, the lower R23 branch calibration yields metallicities approximately 1/7 solar, consistent with the DLA absorption metallicities at low redshifts. In this case, the absorption selected galaxies would lie significantly lower than the luminosity-metallicity relation for emission-line galaxies at z<0.5. We discuss the implications and possible solutions for each scenario.