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Paper: GMRT Observations of HI in Absorption
Volume: 240, Gas and Galaxy Evolution: A Conference in Honor of the 20th Anniversary of the VLA
Page: 43
Authors: Chengalur, J. N.
Abstract: I report here on HI 21 cm absorption observations made using the Giant Metrewave Radio Telescope (GMRT) in the redshift range z ~ 0 to 0.6. The z = 0 observations are of nearby high peculiar velocity clouds in the Milky Way, which are detected in 21 cm absorption for the first time. The low 21 cm optical depths and anomalous Na I/Ca II ratios of these clouds are consistent with them being small clouds shocked by expanding supernova remnants. The results of a survey for 21 cm absorption from low redshift damped Lyα systems (DLAS) is also discussed. Five out of a total of 10 observed systems have been detected in 21 cm absorption. In general DLAS have spin temperatures much higher than that observed in the Milky Way or nearby spiral galaxies. However all DLAS known to arise in spiral galaxies do show low spin temperatures. Our results are consistent with recent optical observations which show that DLA absorption arises in a variety of galaxy types, and not just in large spiral galaxies, and also with models in which the cold phase of the interstellar medium does not develop until z ~ 1.
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