VCC-144 - A STAR-BURSTING DWARF GALAXY IN THE VIRGO CLUSTER

We describe results of a multi-spectral study of a blue compact dwarf galaxy in the Virgo Cluster. The object was observed with broad-band a nd Her imaging, ultraviolet observations, and radio synthesis. Our dat a were combined with previously published optical observations, with H I single-beam observation and with far-infrared data, and were compare d to results of evolutionary synthesis programs. The radio synthesis o bservations revealed a compact concentration of HI coincident with the optical galaxy, embedded in a diffuse, asymmetric HI cloud which has no trace of optical emission. While the overall velocity dispersion an d size of the KI structure suggests that the total mass in stars and g as is not sufficient to gravitationally bind the system as a whole, th e HI clump coincident with the optical galaxy requires little or no da rk matter to be self-gravitating. The diffuse cloud has more complex v elocity structure and is extended in a direction approximately perpend icular to the optical major axis. The optical-UV data can be explained by a single population of stars formed in a recent burst, indicating that this is a genuine young galaxy. The efficiency of star formation is similar to that in large disk galaxies. The IR emission indicates t he presence of dust; this must have been formed very recently, or was already present within the original HI cloud from which the galaxy was formed. The round and smooth isophotes, the correspondence of the opt ical and HI redshifts, and the lack of any suitable nearby galaxy, ind icate that the starburst was probably not triggered by an external int eraction with a visible galaxy. The distribution of HI fits better a b low-out scenario than an accretion or collision with a companion. We p oint out features in common with other actively star-forming dwarf gal axies and conclude that, at least in the southern outskirts of the Vir go cluster, intensive star formation, perhaps for the first time in so me objects, takes place at present.