HI properties and star formation history of a fly-by pair of blue
  compact dwarf galaxies
  A fly-by interaction has been suggested to be one of the major explanations
for enhanced star formation in blue compact dwarf (BCD) galaxies, yet no direct
evidence for this scenario has been found to date. In the HI Parkes all-sky
survey (HIPASS), ESO 435-IG 020 and ESO 435- G 016, a BCD pair were found in a
common, extended gas envelope of atomic hydrogen, providing an ideal case to
test the hypothesis that the starburst in BCDs can be indeed triggered by a
fly-by interaction. Using high-resolution data from the Australia Telescope
Compact Array (ATCA), we investigated HI properties and the spectral energy
distribution (SED) of the BCD pair to study their interaction and star
formation histories. The high-resolution HI data of both BCDs reveal a number
of peculiarities, which are suggestive of tidal perturbation. Meanwhile, 40% of
the HIPASS flux is not accounted for in the ATCA observations with no HI gas
bridge found between the two BCDs. Intriguingly, in the residual of the HIPASS
and the ATCA data, 10% of the missing flux appears to be located between the
two BCDs. While the SED-based age of the most dominant young stellar population
is old enough to have originated from the interaction with any neighbors
(including the other of the two BCDs), the most recent star formation activity
traced by strong H$\alpha$ emission in ESO 435-IG 020 and the shear motion of
gas in ESO 435- G 016, suggest a more recent or current tidal interaction.
Based on these and the residual emission between the HIPASS and the ATCA data,
we propose an interaction between the two BCDs as the origin of their recently
enhanced star formation activity. The shear motion on the gas disk, potentially
with re-accretion of the stripped gas, could be responsible for the active star
formation in this BCD pair.
