Comparative Properties of Virgo Cluster Dwarf Irregulars and Spirals

January 1988 • 1988ApJ...324...75H

Authors • Hoffman, G. Lyle • Helou, George • Salpeter, E. E.

Abstract • We analyze the optical and neutral hydrogen data for all spiral and late-type dwarf irregular galaxies in the Virgo Cluster catalog. In particular, we examine the continuity of optical properties, hydrogen masses, and dynamical properties as functions of morphology and luminosity from the largest spirals through the faintest dwarfs (omitting blue compact dwarf galaxies); the effects of environment on H I content; mass segregation; and the Tully-Fisher relations. The spiral plus dwarf sample forms a continuous but nonhomologous sequence. Indicative dynamical mass-to-light ratios (obtained from central beam H I profile widths and optical radii) are relatively constant throughout; hydrogen mass-to-light ratios show only a slight increase with decreasing luminosity. The Tully-Fisher relations extend with continuous slope from spirals through dwarfs. The dwarfs show some evidence of ram-pressure stripping by the intracluster medium, but as a group do not seem to be stripped more heavily than spirals. There is no evidence of mass segregation even for the very low mass dwarfs versus giant spirals. Some recent theories of the formation of dwarf galaxies are discussed in the light of this analysis.

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George Helou

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