| Abstract | The extended neutral hydrogen envelope of the late-type galaxy NGC 5236 (M83) is investigated. The galaxy was observed in the 21-cm line with the 100-m Effelsberg radio telescope at a half-power beam width of 9 arcmin. Neutral hydrogen is found in an asymmetrical distribution at heliocentric velocities from 324 to 687 km/sec. A measured total extent of 76 x 94.6 arcmin makes the H I envelope one of the largest yet observed, and implies a total H I mass of 2.4 x 10 to the 10th solar masses. Observations are consistent with a warped disk connecting regular inner and outer velocity fields. Data can best be fit by a two-component model with a central depression with a rotation curve of the Brandt type with maximum rotation velocity of 180 km/sec, turnover radius of 4.5 arcmin and shape parameters of 0.3 and 1.5 for the northern and southern parts, respectively. It is noted that, in contrast to most galaxies, M83 has about 80% of its H I outside the Hoolmberg limit. |
