New HI 21-cm absorbers at low and intermediate redshifts

We present the results of a survey for intervening HI 21-cm absorbers at intermediate and low redshift (0<z<1.2). For our total sample of 24 systems, we obtained high quality data for 17 systems, the other seven being severely affected by radio frequency interference (RFI). Five of our targets are low redshift (z<0.17) optical galaxies with small impact parameters (<20 kpc) toward radio-bright background sources. Two of these were detected in 21-cm absorption, showing narrow, high optical depth absorption profiles, the narrowest having a velocity dispersion of only 1.5 km/s, which puts an upper limit on the kinetic temperature of T_k<270 K. Combining our observations with results from the literature, we measure a weak anti-correlation between impact parameter and integral optical depth in local (z<0.5) 21-cm absorbers. Of eleven CaII and MgII systems searched, two were detected in 21-cm absorption, and six were affected by RFI to a level that precludes a detection. For these two systems at z~0.6 we measure spin temperatures of T_s=(65+/-17) K and T_s>180 K. A subset of our systems were also searched for OH absorption, but no detections were made.

Are the kinematics of DLAs in agreement with their arising in the gas disks of galaxies?

We demonstrate in this paper that the velocity widths of the neutral gas in Damped Ly Alpha (DLA) systems are inconsistent with these systems originating in gas disks of galaxies similar to those seen in the local Universe. We examine the gas kinematics of local galaxies using the high quality HI 21-cm data from the HI Nearby Galaxies Survey (THINGS) and make a comparison with the velocity profiles measured in the low-ionization metal lines observed in DLAs at high redshifts. The median velocity width of z=0 HI gas above the DLA column density limit of N=2x10^20 cm-2 is approximately 30 km/s, whereas the typical value in DLAs is a factor of two higher. We argue that the gas kinematics at higher redshifts are increasingly influenced by gas that is not participating in ordered rotation in cold disks, but is more likely associated with tidal gas related to galaxy interactions or processes such as superwinds and outflows. An analysis of the HI in the local interacting star-burst galaxy M82 shows that the velocity widths in this galaxy are indeed similar to what is seen in DLAs.