|Description:|| While it is well established that MgII absorbers and damped Lyman-alpha absorbers (DLAs) seen in the spectra of distant QSOs arise from the gas associated with galaxies, the exact nature and the underlying physical processes driving the physical and chemical state of the absorbing gas is still a matter of debate. A systematic survey of 21-cm absorption in a sample of MgII absorbers and DLAs towards the radio loud quasars allows us to measure the fraction of cold gas associated with these absorbers and investigate the physical conditions in the interstellar medium of distant galaxies.|
In a paper, now accepted for publication in A&A, we report 4 new detections of 21-cm absorption from a systematic search of 21-cm absorption in a sample of MgII absorbers at 0.5 < z < 1.5. The survey is based on data from GBT, GMRT, VLBA and WSRT.
We show that within the measurement uncertainty, the 21-cm detection rate in strong MgII systems is constant over 0.5 < z < 1.5. Since stellar feedback processes are expected to diminish the filling factor of cold neutral medium over 0.5 < z < 1, this lack of evolution in the 21-cm detection rate in strong MgII absorbers is intriguing. We also find that the 21-cm absorption detection rate in the DLAs at z > 2 is at most a factor of 3 less than the upper limits we obtain using the MgII absorbers at 0.5 < z < 1.0. This would imply that either the cross section of 21-cm absorbing gas amongst DLAs has increased from z=3.5 to z=0.5 or that a significant fraction of 21-cm absorbers at 0.5 < z < 1.0 arise from sub-DLAs.
"Search for cold gas in strong MgII absorbers at 0.5 < z < 1.5: nature and evolution of 21-cm absorbers" N. Gupta, R. Srianand, P. Petitjean, J. Bergeron, P. Noterdaeme, and S. Muzahid, A&A accepted