Dwarf-Dwarf Interactions Can Both Trigger and Quench Star Formation

It is exceedingly rare to find quiescent low-mass galaxies in the field. UGC5205 is an example of such a quenched field dwarf (M-star similar to 3x10(8)M(circle dot)). Despite a wealth of cold gas (M-HI similar to 3.5x10(8)M(circle dot)) and GALEX emission that indicates significant star formation in the past few hundred Myr, there is no detection of H alpha emission -- star formation in the last similar to 10 Myr -- across the face of the galaxy. Meanwhile, the near equal-mass companion of UGC5205, PGC027864, is starbursting (EWH alpha>1000 Angstrom). In this work, we present new Karl G. Jansky Very Large Array (VLA) 21 cm line observations of UGC5205 that demonstrate that the lack of star formation is caused by an absence of HI in the main body of the galaxy. The HI of UGC5205 is highly disturbed; the bulk of the HI resides in several kpc-long tails, while the HI of PGC027864 is dominated by ordered rotation. We model the stellar populations of UGC5205 to show that, as indicated by the UV-H alpha emission, the galaxy underwent a coordinated quenching event similar to 100-300 Myr ago. The asymmetry of outcomes for UGC5205 and PGC027864 demonstrate that major mergers can both quench and trigger star formation in dwarfs. However, because the gas remains bound to the system, we suggest that such mergers only temporarily quench star formation. We estimate a total quenched time of similar to 560 Myr for UGC5205, consistent with established upper limits on the quenched fraction of a few percent for dwarfs in the field.