Abstract
A scaling relation has recently been suggested to combine the galaxy
mass-metallicity relation with metallicities of damped Lyman-alpha 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. Assuming that the difference between the
predicted and measured stellar masses is due to a metallicity gradient in the
gaseous discs or halos around the galaxies, we derive an expansion of the
scaling relation to include the DLA metallicity, redshift, and metallicity
gradient. The average metallicity gradient in a DLA galaxy is -0.022+/-0.002
dex/kpc consistent with gradients measured in disc galaxies at similar
redshifts. By including a metallicity gradient in the scaling relation the
scatter reduces to 0.41 dex in log M_*,DLA. We provide a prescription how to
calculate the stellar mass (M_*,DLA) of the galaxy when the DLA metallicity and
DLA galaxy impact parameter is known.
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