The evolution of dwarf galaxies in the Coma supercluster
  We employ spectroscopic and photometric data from SDSS DR7, in a 500 sq
degree region, to understand the evolution of dwarf (~M*+2<M_z<M*+4) galaxies
in the Coma supercluster (z=0.023). We show that in the Coma supercluster, the
red dwarfs are mostly concentrated in the dense cores of the Coma and Abell
1367 clusters, and in the galaxy groups embedded in the filament connecting
them. The post-starburst (k+A) dwarfs however are found in the infall regions
of the Coma and Abell 1367 clusters, and occasionally in galaxy groups embedded
along the filament, suggesting that strong velocity fields prevalent in the
vicinity of deep potential wells may be closely related to the mechanism(s)
leading to the post-starburst phase in dwarf galaxies. Moreover, the blue
colour of some k+A dwarfs in the Coma cluster, found within its virial radius,
suggests that the star formation in these galaxies was quenched very rapidly in
the last 500 Myr. More than 60% of all red dwarf galaxies in the supercluster
have 0-3 ang of H_\delta in absorption, which suggests that a major episode of
star formation occurred in a non-negligible fraction of these galaxies, ending
within the last Gyr, allowing them to move to the red sequence. The
distribution of the blue dwarf galaxies in the Coma supercluster is bimodal in
the EW(H_\alpha)-EW(H_\delta) plane, with one population having very high
emission in H_\alpha, and some emission in H_\delta. A sub-population of blue
dwarfs is coincident with the red dwarfs in the EW(H_\alpha)-EW(H_\delta)
plane, showing absorption in H_\delta and relatively lower emission in
H_\alpha. We suggest that a large fraction of the latter population are the
progenitors of the passive dwarf galaxies that are abundantly found in the
cores of low-redshift rich clusters such as Coma.
