AN INFRARED STUDY OF DWARF GALAXIES IN THE VIRGO CLUSTER

JHK surface photometry is presented for a total of 13 dwarf irregular (dI) and dwarf elliptical (dE) galaxies in the Virgo cluster, drawn from the bright end of the dwarf luminosity function. These images are used to show that the structures defined by the old stellar populations differ significantly between the two types of dwarfs. In particular, the dIs have more flattened and asymmetric stellar light distributions, and there are no dIs with H-band luminosities or surface brightnesses as high as those of the brightest dEs. This is strong evidence against the models in which dEs are formed by the gas-stripping of dIs. However, a tight surface brightness-luminosity relation is found in the H-band, with a scatter of only 0.25 mag, including dwarfs of both types. This is potentially a very powerful redshift-independent distance indicator. One of the galaxies studied, IC 3328, is found to have a prominent nucleus with significantly redder near-IR colours than the remainder of the galaxy.