The Effect of Galaxy Interactions on Molecular Gas Properties
  Galaxy interactions are often accompanied by an enhanced star formation rate
(SFR). Since molecular gas is essential for star formation, it is vital to
establish whether, and by how much, galaxy interactions affect the molecular
gas properties. We investigate the effect of interactions on global molecular
gas properties by studying a sample of 58 galaxies in pairs and 154 control
galaxies. Molecular gas properties are determined from observations with the
JCMT, PMO, CSO telescopes, and supplemented with data from the xCOLD GASS and
JINGLE surveys at $^{12}$CO(1-0) and $^{12}$CO(2-1). The SFR, gas mass
($M_\mathrm{H_{2}}$), and gas fraction ($f_{gas}$) are all enhanced in galaxies
in pairs by $\sim$ 2.5 times compared to the controls matched in redshift,
mass, and effective radius, while the enhancement of star formation efficiency
(SFE $\equiv$ SFR/$M_{H_{2}}$) is less than a factor of 2. We also find that
the enhancements in SFR, $M_{H_{2}}$ and $f_{gas}$ increase with decreasing
pair separation and are larger in systems with smaller stellar mass ratio.
Conversely, the SFE is only enhanced in close pairs (separation $<$ 20 kpc) and
equal-mass systems; therefore most galaxies in pairs lie in the same parameter
space on the SFR-$M_{H_{2}}$ plane as controls. This is the first time that the
dependence of molecular gas properties on merger configurations is probed
statistically with a relatively large sample and with a carefully-selected
control sample for individual galaxies. We conclude that galaxy interactions do
modify the molecular gas properties, although the strength of the effect is
merger configuration dependent.
