Compact dwarf galaxies are an established constituent of the population of lower luminosity galaxies, alongside the more numerous dwarf irregular, dwarf elliptical, and dwarf spheroidal galaxies.
Among compact dwarfs, early-type compact elliptical galaxies such as M32, showing early-type galaxy spectra, are rare, and only very few examples have been found.
Blue compact dwarfs show active star formation superposed on an older, low surface brightness component and have a broad range of sizes, including a very small proportion
with effective radii as small as 300 pc.
Using follow-up data from the Wide Field Camera on the INT, astronomers discovered nine ultracompact dwarf galaxies (UCDs) in the Virgo Cluster, extending samples of these objects outside the Fornax Cluster. The newly found UCDs are
comparable to the UCDs in the Fornax Cluster, with sizes ~<100 pc, -12.9<MB < -10.7, and exhibiting red absorption-line spectra, indicative of an older stellar population.
The properties of these objects remain consistent with the tidal threshing model for the origin of UCDs from the surviving nuclei of nucleated dwarf elliptical galaxies disrupted in the cluster core
but can also be explained as objects that were formed by mergers of star clusters created in galaxy interactions.
The discovery that UCDs exist in Virgo shows that this galaxy type is probably a ubiquitous phenomenon in clusters of galaxies; coupled with their possible origin by tidal threshing, the
UCD population is a potential indicator and probe of the formation history of a given cluster.
A 30"×30" region around Virgo UCD 6 is shown based on a 25 minute B-band integration with the INT Wide Field Camera.
(Extracted from Jones et al., 2006, AJ, 131, 312). [ JPEG | TIFF ]