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Date and Time of the Query: 2019-03-18 T14:58:02 PDT
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For refcode 1971A&A....10..437B:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1971A&A....10..437B The Large-scale Spatial Distribution of Neutral Hydrogen in Galaxies Bottinelli, L. The 21-cm line profile of neutral atomic hydrogen has been measured with the Nancay radio telescope, at several points, in 36 relatively distant (up to 15 Mpc) galaxies from Lenticular to Irregular types The neutral hydrogen has been found displaced by a significant fraction (~=1/3) of a beamwidth with respect to the optical centre, in about 40% of the galaxies, These asymmetrical distributions do not seen always correlated with the presence of neighbouring galaxies. The large-scale H I distributions have been characterized by H I diameters. The ratio of this H I diameter to the optical one has been found correlated with the type: it increases by about a factor of 2 when going from types Sb to Irregular. The large-scale distribution of the H I projected density has been studied for 33 galaxies. Its consistency with a ring-like model has been investigated: in 1/3 of the cases it appears suitable. The variation of the H I to optical diameters ratio with the type allows the determination of an intrinsic mean H I projected density which is found to be rather independent of the type. It is shown that the variation with the type of the usually adopted mean H I projected density reflects, in fact, the correlation existing between the H I to optical diameters ratio and the type. The neutral hydrogen seems to be more strongly concentrated towards the central regions in the Sb galaxies than in the Sm and Irr ones. A gaussian distribution of the H I volumic distribution density being assumed,the optical limit of a galaxy seems to be characterized by the same range of H I volumic density values, for all morphological types, which corresponds possibly to about a same low rate of star formation. Key words: galaxies-radio radiation-21-cm radiation-interstellar matter
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