Mass and metallicity scaling relations of high redshift star-forming
  galaxies selected by GRBs
  We present a comprehensive study of the relations between gas kinematics,
metallicity, and stellar mass in a sample of 82 GRB-selected galaxies using
absorption and emission methods. We find the velocity widths of both emission
and absorption profiles to be a proxy of stellar mass. We also investigate the
velocity-metallicity correlation and its evolution with redshift and find the
correlation derived from emission lines to have a significantly smaller scatter
compared to that found using absorption lines. Using 33 GRB hosts with measured
stellar mass and metallicitiy, we study the mass-metallicity relation for GRB
host galaxies in a stellar mass range of $10^{8.2} M_{\odot}$ to $10^{11.1}
M_{\odot}$ and a redshift range of $ z\sim 0.3-3.4$. The GRB-selected galaxies
appear to track the mass-metallicity relation of star forming galaxies but with
an offset of 0.15 towards lower metallicities. This offset is comparable with
the average error-bar on the metallicity measurements of the GRB sample and
also the scatter on the MZ relation of the general population. It is hard to
decide whether this relatively small offset is due to systematic effects or the
intrinsic nature of GRB hosts. We also investigate the possibility of using
absorption-line metallicity measurements of GRB hosts to study the
mass-metallicity relation at high redshifts. Our analysis shows that the
metallicity measurements from absorption methods can significantly differ from
emission metallicities and assuming identical measurements from the two methods
may result in erroneous conclusions.
