2015MNRAS.450.2473L

Using multiwavelength kinematic and photometric data we have analysed the gaseous and stellar properties of a previously uncharacterized low-mass star-forming companion and newly discovered stellar stream seen projected against the edge-on spiral galaxy NGC 7241. The companion object was identified serendipitously as an offset velocity component in H α Fabry-Perot observations along the line of sight to NGC 7241, and is most prominent visually in UV and blue wavelengths. Its occulting position with respect to NGC 7241 allows measurement of its dust extinction properties which are then combined with photometric spectral energy distribution fitting and long-slit spectroscopy to study star formation (SF) in this gas-rich accreting dwarf galaxy. The dynamical properties of the stream and companion suggest that they may likely be remnants of the same low-mass progenitor dwarf galaxy which is being disrupted during its accretion on to NGC 7241 - with the companion's recent SF triggered during its passage with the disc of NGC 7241. This is supported by the companion's metallicity and SF rates, the asymmetric SF in the disc of NGC 7241, as well as the coincident velocity of the extraplanar HI filament and the star-forming companion. In contrast, mass estimates from dynamical modelling of NGC 7241 rule out an interaction between NGC 7241 and UGC 11964 (the other large spiral galaxy in the group) within the last ∼ 3 Gyr - making such an interaction a poor candidate for inducing the recent SF in the system. Together, the data for this system offer a window into how SF proceeds in low-mass mergers.