Galaxy Pairs in the Sloan Digital Sky Survey - X: Does gas content alter
  star formation rate enhancement in galaxy interactions?
  New spectral line observations, obtained with the Jansky Very Large Array
(VLA), of a sample of 34 galaxies in 17 close pairs are presented in this
paper. The sample of galaxy pairs is selected to contain galaxies in close,
major interactions (i.e., projected separations $<$30 kpc/h, and mass ratios
less extreme than 4:1), while still having a sufficiently large angular
separation that the VLA can spatially resolve both galaxies in the pair. Of the
34 galaxies, 17 are detected at $> 3\sigma$. We compare the HI gas fraction of
the galaxies with the triggered star formation present in that galaxy. When
compared to the star formation rates (SFRs) of non-pair galaxies matched in
mass, redshift, and local environment, we find that the star formation
enhancement is weakly positively correlated ($\sim 2.5\sigma$) with HI gas
fraction. In order to help understand the physical mechanisms driving this weak
correlation, we also present results from a small suite of binary galaxy merger
simulations with varying gas fractions. The simulated galaxies indicate that
larger initial gas fractions are associated with lower levels of
interaction-triggered star formation (relative to an identical galaxy in
isolation), but also show that high gas fraction galaxies have higher absolute
SFRs prior to an interaction. We show that when interaction-driven SFR
enhancements are calculated relative to a galaxy with an average gas fraction
for its stellar mass, the relationship between SFR and initial gas fraction
dominates over the SFR enhancements driven by the interaction. Simulated galaxy
interactions that are matched in stellar mass but not in gas fraction, like our
VLA sample, yield the same general positive correlation between SFR enhancement
and gas fraction that we observe.
