Prevalence of neutral gas in centres of merging galaxies
  We present Giant Metrewave Radio Telescope and Very Large Array observations
of HI 21-cm absorption in ten z<=0.2 galaxy mergers that host strong radio
sources. Seven of these mergers show strong absorption [with N(HI) ~10^{21-22}
cm^{-2}, for spin temperature of 100 K and unit covering factor], leading to a
total detection rate of 83 +/- 17% in low-z radio-loud galaxy mergers. This is
~3-4 times higher than that found for intrinsic HI 21-cm absorption in low-z
radio sources in general. The fraction of intrinsic absorbers that are
associated with mergers increases with increasing N(HI) threshold, i.e. ~40%
and 100% of the absorbers with N(HI) >10^{21} cm^{-2} and >10^{22} cm^{-2}
arise from mergers, respectively. The distribution of N(HI) among the mergers
is significantly different from that found in isolated systems, with mergers
giving rise to six times stronger absorption on average. The fraction of
redshifted absorption components (with respect to the systemic velocity of the
radio source obtained from optical emission lines) among mergers is found to be
higher by two to three times compared to that found for non-interacting
systems. Follow-up spatially-resolved multi-wavelength spectroscopy is
essential to understand the exact connection between the presence of
circumnuclear neutral gas and the AGN activity in these mergers.
