  It has long been speculated that many starburst or compact dwarf galaxies are
resulted from dwarf-dwarf galaxy merging, but unequivocal evidence for this
possibility has rarely been reported in the literature. We present the first
study of deep optical broadband images of a gas-dominated blue compact dwarf
galaxy (BCD) VCC848 (Mstar=2e8Msun) which hosts extended stellar shells and
thus is confirmed to be a dwarf-dwarf merger. VCC848 is located in the
outskirts of the Virgo Cluster. By analyzing the stellar light distribution, we
found that VCC848 is the result of a merging between two dwarf galaxies with a
primary-to-secondary mass ratio < ~ 5 for the stellar components and < ~ 2 for
the presumed dark matter halos. The secondary progenitor galaxy has been almost
entirely disrupted. The age-mass distribution of photometrically selected star
cluster candidates in VCC848 implies that the cluster formation rate (CFR,
proportional to star formation rate) was enhanced by a factor of ~ 7 - 10
during the past 1 Gyr. The merging-induced enhancement of CFR peaked near the
galactic center a few hundred Myr ago and has started declining in the last few
tens of Myr. The current star formation activities, as traced by the youngest
clusters, mainly occur at large galactocentric distances (> ~ 1 kpc). The fact
that VCC848 is still (atomic) gas-dominated after the period of most violent
collision suggests that gas-rich dwarf galaxy merging can result in BCD-like
remnants with extended atomic gas distribution surrounding a blue compact
center, in general agreement with previous numerical simulations.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics