Interstellar Medium and Star Formation of Starburst Galaxies on the
  Merger Sequence
  The interstellar medium is a key ingredient that governs star formation in
galaxies. We present a detailed study of the infrared (~ 1-500 micron) spectral
energy distributions of a large sample of 193 nearby (z ~ 0.088) luminous
infrared galaxies (LIRGs) covering a wide range of evolutionary stages along
the merger sequence. The entire sample has been observed uniformly by 2MASS,
WISE, Spitzer, and Herschel. We perform multi-component decomposition of the
spectra to derive physical parameters of the interstellar medium, including the
intensity of the interstellar radiation field and the mass and luminosity of
the dust. We also constrain the presence and strength of nuclear dust heated by
active galactic nuclei. The radiation field of LIRGs tends to have much higher
intensity than in quiescent galaxies, and it increases toward advanced merger
stages as a result of central concentration of the interstellar medium and star
formation. The total gas mass is derived from the dust mass and the galaxy
stellar mass. We find that the gas fraction of LIRGs is on average ~ 0.3 dex
higher than that of main-sequence star-forming galaxies, rising moderately
toward advanced merger stages. All LIRGs have star formation rates that place
them above the galaxy star formation main sequence. Consistent with recent
observations and numerical simulations, the global star formation efficiency of
the sample spans a wide range, filling the gap between normal star-forming
galaxies and extreme starburst systems.
