Probing dust-obscured star formation in the most massive Gamma-Ray Burst
  host galaxies
  Due to their relation to massive stars, long-duration gamma-ray bursts (GRBs)
allow pinpointing star formation in galaxies independently of redshift, dust
obscuration, or galaxy mass/size, thus providing a unique tool to investigate
the star-formation history over cosmic time. About half of the optical
afterglows of long-duration GRBs are missed due to dust extinction, and are
primarily located in the most massive GRB hosts. In order to understand this
bias it is important to investigate the amount of obscured star-formation in
these GRB host galaxies. Radio emission of galaxies correlates with
star-formation, but does not suffer extinction as do the optical star-formation
estimators. We selected 11 GRB host galaxies with either large stellar mass or
large UV-/optical-based star-formation rates (SFRs) and obtained radio
observations of these with the Australia Telescope Compact Array and the Karl
Jansky Very Large Array. Despite intentionally selecting GRB hosts with
expected high SFRs, we do not find any star-formation-related radio emission in
any of our targets. Our upper limit for GRB 100621A implies that the earlier
reported radio detection was due to afterglow emission. We do detect radio
emission from the position of GRB 020819B, but argue that it is in large parts,
if not all, due to afterglow contamination. Half of our sample has
radio-derived SFR limits which are only a factor 2--3 above the optically
measured SFRs. This supports other recent studies that the majority of star
formation in GRB hosts is not obscured by dust.
