First measurement of HI 21cm emission from a GRB host galaxy indicates a
  post-merger system
  We report the detection and mapping of atomic hydrogen in HI 21cm emission
from ESO 184-G82, the host galaxy of the gamma ray burst 980425. This is the
first instance where HI in emission has been detected from a galaxy hosting a
gamma ray burst. ESO 184-G82 is an isolated galaxy and contains a Wolf-Rayet
region close to the location of the gamma ray burst and the associated
supernova, SN 1998bw. This is one of the most luminous HII regions identified
in the local Universe, with a very high inferred density of star formation. The
HI 21cm observations reveal a high HI mass for the galaxy, twice as large as
the stellar mass. The spatial and velocity distribution of the HI 21cm emission
reveals a disturbed rotating gas disk, which suggests that the galaxy has
undergone a recent minor merger that disrupted its rotation. We find that the
Wolf-Rayet region and the gamma ray burst are both located in the highest HI
column density region of the galaxy. We speculate that the merger event has
resulted in shock compression of the gas, triggering extreme star formation
activity, and resulting in the formation of both the Wolf-Rayet region and the
gamma ray burst. The high HI column density environment of the GRB is
consistent with the high HI column densities seen in absorption in the host
galaxies of high redshift gamma ray bursts.
