Tidal Tails of Minor Mergers: Star Formation Efficiency in the Western
  Tail of NGC 2782
  While major mergers and their tidal debris are well studied, they are less
common than minor mergers (mass ratios < 0.3). The peculiar spiral NGC 2782 is
the result of a merger between two disk galaxies with a mass ratio of ~4:1
occurring ~200 Myr ago. This merger produced a molecular and H I-rich,
optically bright eastern tail and an H I-rich, optically faint western tail.
Non-detection of CO in the western tail by Braine et al. suggested that star
formation had not yet begun to occur in that tidal tail. However, deep
H{\alpha} narrowband images show evidence of recent star formation in the
western tail. Across the entire western tail, we find the global star formation
rate per unit area ({\Sigma}SFR) to be several orders of magnitude less than
expected from the total gas density. Together with extended FUV+NUV emission
from Galaxy Evolution Explorer along the tail, this indicates a low global star
formation efficiency in the tidal tail producing lower mass star clusters. The
H II region that we observed has a local (few-kiloparsec scale) {\Sigma}SFR
from H{\alpha} that is less than that expected from the total gas density,
which is consistent with other observations of tidal debris. The star formation
efficiency of this H II region inferred from the total gas density is low, but
normal when inferred from the molecular gas density. These results suggest the
presence of a very small, locally dense region in the western tail of NGC 2782
or of a low-metallicity and/or low-pressure star-forming region.
