Inverted metallicity gradients in two Virgo cluster star-forming dwarf
  galaxies: evidence of recent merging?
  We present integral field spectroscopy observations of two star-forming dwarf
galaxies in the Virgo cluster (VCC135 and VCC324) obtained with PMAS/PPak at
the Calar Alto 3.5 meter telescope. We derive metallicity maps using the N2
empirical calibrator. The galaxies show positive gas metallicity gradients,
contrarily to what is usually found in other dwarfs or in spiral galaxies. We
measure gradient slopes of 0.20 $\pm$ 0.06 and 0.15 $\pm$ 0.03 dex/$R_e$ for
VCC135 and VCC324, respectively. Such a trend has been only observed in few,
very isolated galaxies, or at higher redshifts ($z >$ 1). It is thought to be
associated with accretion of metal-poor gas from the intergalactic medium, a
mechanism that would be less likely to occur in a high-density environment like
Virgo. We combine emission line observations with deep optical images to
investigate the origin of the peculiar metallicity gradient. The presence of
weak underlying substructures in both galaxies and the analysis of
morphological diagnostics and of ionised gas kinematics suggest that the inflow
of metal-poor gas to the central regions of the dwarfs may be related to a
recent merging event with a gas-rich companion.
