New H I 21-cm absorbers at low and intermediate redshifts
Résumé
We present the results of a survey for intervening HI 21-cm absorbers at intermediate and low redshift (0 \textless z \textless 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 \textless 0.17) optical galaxies with small impact parameters (\textless 20 kpc) towards 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(-1), which puts an upper limit on the kinetic temperature of T-k \textless 270 K. Combining our observations with results from the literature, we measure a weak anticorrelation between impact parameter and integral optical depth in local (z \textless 0.5) 21-cm absorbers. Of 11 Ca II and Mg II 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 similar to 0.6, we measure spin temperatures of T-s = (65 +/- 17) K and T-s \textgreater 180 K. A subset of our systems was also searched for OH absorption, but no detections were made.
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