A Search for Redshifted HI 21cm Absorption by Damped Ly-alpha Absorption Systems

Details A Search for Redshifted HI 21cm Absorption by Damped Ly-alpha Absorption Systems A Search for Redshifted HI 21cm Absorption by Damped Ly-alpha Absorption Systems

Dec 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...187.8505l&link_type=abstract

American Astronomical Society, 187th AAS Meeting, #85.05; Bulletin of the American Astronomical Society, Vol. 27, p.1412

Astronomy and Astrophysics

Astronomy

Scientific paper

Using data from the recently upgraded WSRT we search for HI 21cm absorption associated with three high redshift damped Lyalpha systems. We detect no absorption at higher than a 3sigma level in any object. We calculate a lower limit on the temperatures of the absorbing gas by comparing column densities in HI derived from HI 21 cm absorption with those derived from damped Lyalpha absorption, and combine our results with previous HI 21 cm observations of damped Lyalpha systems. We find a typical value for the harmonic mean spin temperature of gas in such systems of: ~ 10(3) K. We compare results from damped Lyalpha systems to results for Galactic gas and gas in M31, using a standard - tau relationship (Braun and Walterbos, 1992). We see that at a given optical depth, the values of for the damped Lyalpha systems are systematically higher than those for the Galaxy by about a factor of 5. This suggests, in a two phase medium, either a larger amount of warm gas than is found in the Galaxy, a higher temperature for the cold phase than is found in the Galaxy, or a combination of the two. The data at low opacity, or high radius (R > 15kpc) for M31 converge with the damped Lyalpha data, suggesting that conditions in the damped Lyalpha sytems may be similar to those found in the outer reaches of galaxies. We also search for HI 21cm emission and find none at a 5sigma or higher level in the fields of any of the sources. We derive an upper limit on the mass of Hydrogen present in the system which effectively rules out the possibility that any of these systems are proto-clusters according to the model defined by Oort (1984). Finally we find a molecular hydrogen fraction in the system towards 0528-2505, of F = 2N(H_2)/N(HI) > 2%. References: Braun and Walterbos, 1992 Ap.J., 157, 1055 Oort, 1984, A.A., 139, 211

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