Abstract
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.
Highlights
While the spectral energy distributions (SED)-based age of the most dominant young stellar population is old enough to have originated from the interaction with any neighbors, the most recent star formation activity traced by strong Hα 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 Hi Parkes all-sky survey (HIPASS) and the ATCA data, we propose an interaction between the two blue compact dwarf (BCD) as the origin of their recently enhanced star formation activity
Blue compact dwarf galaxies (BCDs) are low-mass systems characterized by active star formation in compact regions and strong narrow emission lines superposed on a flat stellar continuum (e.g., Salzer et al 1989; Kehrig et al 2004)
The goal was to find the evidence for fly-by interaction between the pair as suggested by a large Hi envelope covering both that is found by the HIPASS, and to investigate the role of tidal interaction in triggering recent active star formation in the pair
Summary
Blue compact dwarf galaxies (BCDs) are low-mass systems characterized by active star formation in compact regions and strong narrow emission lines superposed on a flat stellar continuum (e.g., Salzer et al 1989; Kehrig et al 2004). They were originally considered as either nascent or immature galaxies that had recently undergone intense bursts of star formation (Searle et al 1973). A number of models have shown that dwarf galaxies may go through a “BCD phase” due to the gas infall (e.g., Verbeke et al 2014), merging with another dwarf galaxy (e.g., Di Matteo et al 2007; Bekki 2008; Cloet-Osselaer et al 2014), or fly-by interaction (e.g., Icke 1985; Pustilnik et al 2001)
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