Verifying the mass-metallicity relation in damped Lyman α selected galaxies at 0.1 < z < 3.2

A scaling relation has recently been suggested to combine the galaxy mass-metallicity (MZ) relation with metallicities of damped Lyman α systems (DLAs) in quasar spectra. Based on this relation the stellar masses of the absorbing galaxies can be predicted. We test this prediction by measuring the stellar masses of 12 galaxies in confirmed DLA absorber-galaxy pairs in the redshift range 0.1 < z < 3.2. We find an excellent agreement between the predicted and measured stellar masses over three orders of magnitude, and we determine the average offset <C_[M/H]> = 0.44 ± 0.10 between absorption and emission metallicities. We further test if C_[M/H] could depend on the impact parameter and find a correlation at the 5.5σ level. The impact parameter dependence of the metallicity corresponds to an average metallicity difference of -0.022 ± 0.004 dex kpc^-1. By including this metallicity versus impact parameter correlation in the prescription instead of C_[M/H], the scatter reduces to 0.39 dex in log M_*. We provide a prescription on how to calculate the stellar mass (M_*^{DLA}) of the galaxy when both the DLA metallicity and DLA galaxy impact parameter is known. We demonstrate that DLA galaxies follow the MZ relation for luminosity-selected galaxies at z = 0.7 and 2.2 when we include a correction for the correlation between impact parameter and metallicity.