We present the results from our survey of H i 21-cm absorption , using GMRT , VLA and WSRT , in a sample of 55 z < 0.4 galaxies towards radio sources with impact parameters ( b ) in the range \sim 0 - 35 kpc .
In our primary sample ( defined for statistical analyses ) of 40 quasar-galaxy-pairs ( QGPs ) , probed by 45 sightlines , we have found seven H i 21-cm absorption detections , two of which are reported here for the first time .
Combining our primary sample with measurements having similar optical depth sensitivity ( \int \tau dv \leq 0.3 km s ^ { -1 } ) from the literature , we find a weak anti-correlation ( rank correlation coefficient = - 0.20 at 2.42 \sigma level ) between \int \tau dv and b , consistent with previous literature results .
The covering factor of H i 21-cm absorbers ( C _ { 21 } ) is estimated to be 0.24 ^ { +0.12 } _ { -0.08 } at b \leq 15 kpc and 0.06 ^ { +0.09 } _ { -0.04 } at b = 15 - 35 kpc . \int \tau dv and C _ { 21 } show similar declining trend with radial distance along the galaxy ’ s major axis and distances scaled with the effective H i radius .
There is also tentative indication that most of the H i 21-cm absorbers could be co-planar with the extended H i discs .
No significant dependence of \int \tau dv and C _ { 21 } on galaxy luminosity , stellar mass , colour and star formation rate is found , though the H i 21-cm absorbing gas cross-section may be larger for the luminous galaxies .
The higher detection rate ( by a factor of \sim 4 ) of H i 21-cm absorption in z < 1 DLAs compared to the QGPs indicates towards small covering factor and patchy distribution of cold gas clouds around low- z galaxies .