| Popis: |
Large-aperture spectrophotometric observations and CCD images in the H-alpha and R bands have been obtained for Virgo cluster Magellanic, dwarf, and amorphous irregular galaxies. Although a small number of Virgo cluster irregulars have optical and H I properties consistent with recent gas loss, the rate of production of gas-poor irregulars is too low to account for the large population of Virgo cluster dE galaxies or to explain the deficiency in the number of irregulars relative to spirals. Radial brightness profiles reveal that only NGC 4641 follows the r exp 1/4 law of classical ellipticals, that four of the galaxies have exponential brightness distributions, and that one system has an indeterminant profile form. It is shown that the properties of Virgo cluster irregular galaxies can be best understood in terms of environmental modifications of normal systems in the circumcluster environment and in the cluster core. 78 refs. |
