Role of Galaxy Mergers in Cosmic Star Formation History
  We present a morphology study of intermediate-redshift (0.2<z<1.2) luminous
infrared galaxies (LIRGs) and general field galaxies in the GOODS fields using
a revised asymmetry measurement method optimized for deep fields. By taking
careful account of the importance of the underlying sky-background structures,
our new method does not suffer from systematic bias and offers small
uncertainties. By redshifting local LIRGs and low-redshift GOODS galaxies to
different higher redshifts, we have found that the redshift dependence of the
galaxy asymmetry due to surface-brightness dimming is a function of the
asymmetry itself, with larger corrections for more asymmetric objects. By
applying redshift-, IR-luminosity- and optical-brightness-dependent asymmetry
corrections, we have found that intermediate-redshift LIRGs generally show
highly asymmetric morphologies, with implied merger fractions ~50% up to z=1.2,
although they are slightly more symmetric than local LIRGs. For general field
galaxies, we find an almost constant relatively high merger fraction (20-30%).
The B-band LFs of galaxy mergers are derived at different redshifts up to z=1.2
and confirm the weak evolution of the merger fraction after breaking the
luminosity-density degeneracy. The IR luminosity functions (LFs) of galaxy
mergers are also derived, indicating a larger merger fraction at higher IR
luminosity. The integral of the merger IR LFs indicates a dramatic evolution of
the merger-induced IR energy density [(1+z)^(5-6)}], and that galaxy mergers
start to dominate the cosmic IR energy density at z>~1.
