Blue Compact Dwarf Galaxies in the Virgo Cluster: H i and IRAS Data and Upper Limits on Proto--Dwarf Galaxies

April 1989 • 1989ApJ...339..812H

Authors • Hoffman, G. Lyle • Helou, George • Salpeter, E. E. • Lewis, B. Murray

Abstract • Blue compact dwarf (BCD) galaxies in the Virgo Cluster Catalog (VCC) are studied, using existing optical data, our H I observations (both previously published and new), and co-added IRAS data. In addition, we establish upper limits on the number of optically invisible H I clouds within the VCC survey area. We find that our BCDs lie mainly in two clumps: a low heliocentric velocity clump within the central core, which is most likely the same physical association as that formed by the low-velocity spirals that are thought to be falling through the cluster core from behind, and a diffuse cloud centered on the W group, behind and to the south of the cluster core. Our BCDs tend to have rather large H I profile widths; at constant width, the BCDs are comparable to other dwarf irregular galaxies in blue luminosity and H I flux, but the BCDs are significantly smaller (by a factor of 2 or 3) in optical diameter. We suggest that luminosity in a BCD is redistributed rather than increased from that of an Im galaxy of similar size or mass. About one-third of the BCDs were detected at 60 or 100 microns by IRAS after co-addition, mostly at intensities just above the threshold sensitivity. This is a larger detection rate than for other dwarf galaxies at a comparable distance. The correlations of far-infrared (FIR) luminosity against optical and H I properties suggest that the FIR luminosity of BCDs is dominated by emission from the star formation regions, and that their interstellar medium is deficient in dust only by a modest factor of 2 or 3 compared with normal spiral galaxies. We do not find any significant number of H I clouds in the VCC area without accompanying optical emission. This absence of proto-dwarf galaxies, coupled with the presence of significant dust in observed BCDs, argues that most, if not all, of the Virgo BCDs must have experienced star formation prior to the current burst.

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George Helou

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