  Interactions and mergers play an important role in regulating the physical
properties of galaxies, such as their morphology, gas content, and star
formation rate (SFR). Controversy exists as to the degree to which these
events, even gas-rich major mergers, enhance star formation activity. We study
merger pairs selected from a sample of massive ($M_* \ge 10^{10}\,M_\odot$),
low-redshift ($z = 0.01-0.11$) galaxies located in the Stripe 82 region of the
Sloan Digital Sky Survey, using stellar masses, SFRs, and total dust masses
derived from a new set of uniformly measured panchromatic photometry and
spectral energy distribution analysis. The dust masses, when converted to
equivalent total atomic and molecular hydrogen, probe gas masses as low as
$\sim 10^{8.5}\,M_\odot$. Our measurements delineate a bimodal distribution on
the $M_{\rm gas}-M_*$ plane: the gas-rich, star-forming galaxies that trace the
well-studied gas mass main sequence, and passive galaxies that occupy a
distinct, gas-poor regime. These two populations, in turn, map into a bimodal
distribution on the relation between SFR and gas mass surface density. Among
low-redshift galaxies, galaxy mergers, including those that involve gas-rich
and nearly equal-mass galaxies, exert a minimal impact on their SFR, specific
SFR, or star formation efficiency. Starbursts are rare. The star formation
efficiency of gas-rich, minor mergers even appears suppressed. This study
stresses the multiple, complex factors that influence the evolution of the gas
and its ability to form stars in mergers.
