  A large sample of MgII emitting star-forming galaxies with low metallicity
[O/H] = log(O/H)-log(O/H)sun between -0.2 and -1.2 dex is constructed from Data
Release 14 of the Sloan Digital Sky Survey. We selected 4189 galaxies with MgII
2797, 2803 emission lines in the redshift range z~0.3-1.0 or 35% of the total
Sloan Digital Sky Survey star-forming sample with redshift z>0.3. We study the
dependence of the magnesium-to-oxygen and magnesium-to-neon abundance ratios on
metallicity. Extrapolating this dependence to [Mg/Ne]=0 and to solar
metallicity we derive a magnesium depletion of [Mg/Ne]~-0.4 (at solar
metallicity). We prefer neon instead of oxygen to evaluate the magnesium
depletion in the interstellar medium because neon is a noble gas and is not
incorporated into dust, contrary to oxygen. Thus, we find that more massive and
more metal abundant galaxies have higher magnesium depletion. The global
parameters of our sample, such as the mass of the stellar population and star
formation rate, are compared with previously obtained results from the
literature. These results confirm that MgII emission has a nebular origin. Our
data for interstellar magnesium-to-oxygen abundance ratios relative to the
solar value are in good agreement with similar measurements made for Galactic
stars, for giant stars in the Milky Way satellite dwarf galaxies, and with
low-metallicity damped Lyman-alpha systems.
