The host galaxies and explosion sites of long-duration gamma ray bursts:
  Hubble Space Telescope near-infrared imaging
  We present the results of a Hubble Space Telescope WFC3/F160W SNAPSHOT sur-
vey of the host galaxies of 39 long-duration gamma-ray bursts (LGRBs) at z < 3.
We have non-detections of hosts at the locations of 4 bursts. Sufficient
accuracy to as- trometrically align optical afterglow images and determine the
location of the LGRB within its host was possible for 31/35 detected hosts. In
agreement with other work, we find the luminosity distribution of LGRB hosts is
significantly fainter than that of a star formation rate-weighted field galaxy
sample over the same redshift range, indicating LGRBs are not unbiasedly
tracing the star formation rate. Morphologi- cally, the sample of LGRB hosts
are dominated by spiral-like or irregular galaxies. We find evidence for
evolution of the population of LGRB hosts towards lower-luminosity, higher
concentrated hosts at lower redshifts. Their half-light radii are consistent
with other LGRB host samples where measurements were made on rest-frame UV
obser- vations. In agreement with recent work, we find their 80 per cent
enclosed flux radii distribution to be more extended than previously thought,
making them intermedi- ate between core-collapse supernova (CCSN) and
super-luminous supernova (SLSN) hosts. The galactocentric projected-offset
distribution confirms LGRBs as centrally concentrated, much more so than CCSNe
and similar to SLSNe. LGRBs are strongly biased towards the brighter regions in
their host light distributions, regardless of their offset. We find a
correlation between the luminosity of the LGRB explosion site and the intrinsic
column density, N_H , towards the burst.
