The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf-Dwarf Merging: HI
  Gas, Star Formation and Numerical Simulations
  A clear link between a dwarf-dwarf merger event and enhanced star formation
(SF) in the recent past was recently identified in the gas-dominated merger
remnant VCC 848, offering by far the clearest view of a gas-rich late-stage
dwarf-dwarf merger. We present a joint analysis of JVLA HI emission-line
mapping, optical imaging and numerical simulations of VCC 848, in order to
examine the impact of the merger on the stellar and gaseous distributions. VCC
848 has less than 30% of its HI gas concentrated within the central
high-surface-brightness star-forming region, while the remaining HI is
entrained in outlying tidal features. Particularly, a well-defined tidal arm
reaches N(HI) comparable to the galaxy center but lacks SF. The molecular gas
mass inferred from the current SF rate (SFR) dominates over the atomic gas mass
in the central ~ 1.5 kpc. VCC 848 is consistent with being a main-sequence
star-forming galaxy for its current stellar mass and SFR. The HII region
luminosity distribution largely agrees with that of normal dwarf irregulars
with similar luminosities, except that the brightest HII region is
extraordinarily luminous. Our N-body/hydrodynamical simulations imply that VCC
848 is a merger between a gas-dominated primary progenitor and a gas-bearing
star-dominated secondary. The progenitors had their first passage on a
near-radial non-coplanar orbit more than 1 Gyr ago. The merger did not build up
a core as compact as typical compact dwarfs with centralized starburst, which
may be partly ascribed to the star-dominated nature of the secondary, and in a
general sense, a negative stellar feedback following intense starbursts
triggered at early stages of the merger.
