We present ultraviolet (UV) color-magnitude relations (CMRs) of early-type
dwarf galaxies in the Virgo cluster, based on Galaxy Evolution Explorer (GALEX)
UV and Sloan Digital Sky Survey (SDSS) optical imaging data. We find that dwarf
lenticular galaxies (dS0s), including peculiar dwarf elliptical galaxies (dEs)
with disk substructures and blue centers, show a surprisingly distinct and
tight locus separated from that of ordinary dEs, which is not clearly seen in
previous CMRs. The dS0s in UV CMRs follow a steeper sequence than dEs and show
bluer UV-optical color at a given magnitude. We also find that the UV CMRs of
dEs in the outer cluster region are slightly steeper than that of their
counterparts in the inner region, due to the existence of faint, blue dEs in
the outer region. We explore the observed CMRs with population models of a
luminosity-dependent delayed exponential star formation history. We confirm
that the feature of delayed star formation of early-type dwarf galaxies in
Virgo cluster is strongly correlated with their morphology and environment. The
observed CMR of dS0s is well matched by models with relatively long delayed
star formation. Our results suggest that dS0s are most likely transitional
objects at the stage of subsequent transformation of late-type progenitors to
ordinary red dEs in the cluster environment. In any case, UV photometry
provides a powerful tool to disentangle the diverse subpopulations of
early-type dwarf galaxies and uncover their evolutionary histories.Comment: 6 pages, 2 figures, 1 table, accepted for publication in the ApJ