A Morphological Study of Gamma‐Ray Burst Host Galaxies

We present a comprehensive study of the morphological properties of 42gamma-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope inthe optical band. The purpose of this study is to understand the relation ofGRBs to their macro-environments, and to compare the GRB-selected galaxies toother high redshift samples. We perform both qualitative and quantitativeanalyses by categorizing the galaxies according to their visual properties, andby examining their surface brightness profiles. We find that all of thegalaxies have approximately exponential profiles, indicative of galactic disks,and have a median scale length of about 1.7 kpc. Inspection of the visualmorphologies reveals a high fraction of merging and interacting systems, with\~30% showing clear signs of interaction, and an additional ~30% exhibitingirregular and asymmetric structure which may be the result of recent mergers;these fractions are independent of redshift and galaxy luminosity. On the otherhand, the three GRB host galaxies for which submillimeter and radio emissionhas been detected are isolated and compact, unlike the luminoussubmillimeter-selected galaxies. The fraction of mergers appears to be elevatedcompared to other high redshift samples, particularly for the low luminositiesof GRB hosts (M_B ~ -16 to -21 mag). This suggests that merging and interactinggalaxies undergoing a burst of star formation may be an efficient site for theproduction of GRB progenitors. Finally, we show that GRB hosts clearly followthe size-luminosity relation present in other galaxy samples, but thanks toabsorption redshifts they help extend this relation to lower luminosities.Comment: Submitted to ApJ; 7 figures; 2 table