The role of galaxy interaction in the SFR-M relation: characterizing
  morphological properties of Herschel-selected galaxies at 0.2<z<1.5
  Galaxy interactions/mergers have been shown to dominate the population of IR
luminous galaxies (log(LIR)>11.6Lsun) in the local Universe (z<0.25). Recent
studies based on the relation between galaxies' star formation rates and
stellar mass (the SFR-M relation or the galaxy main sequence (MS)) have
suggested that galaxy interaction/mergers may only become significant when
galaxies fall well above the galaxy MS. Since the typical SFR at given M
increases with redshift, the existence of galaxy MS implies that massive,
IR-luminous galaxies at high-z may not necessarily be driven by galaxy
interactions. We examine the role of galaxy interactions in the SFR-M relation
by carrying out a morphological analysis of 2084 Herschel-selected galaxies at
0.2 < z < 1.5 in the COSMOS field. Herschel-PACS and -SPIRE observations
covering the full 2-deg^2 COSMOS field provide one of the largest far-IR
selected samples of high-redshift galaxies with well-determined redshifts to
date, with sufficient sensitivity at z ~ 1, to sample objects lying on and
above the galaxy MS. Using a detailed visual classification scheme, we show
that the fraction of "disk galaxies" decreases and the fraction of "irregular"
galaxies increases systematically with increasing LIR out to z ~ 1.5 and z ~
1.0, respectively. At log(LIR) > 11.5 Lsun, >50% of the objects show evident
features of strongly interacting/merger systems, where this percentage is
similar to the studies of local IR-luminous galaxies. The fraction of
interacting/merger systems also systematically increases with the deviation
from the SFR-M relation, supporting the view that galaxies fall above the MS
are more dominated by mergers than the MS galaxies. Meanwhile, we find that
~18% of massive IR-luminous MS galaxies are classified as interacting systems,
where this population may not evolve through the evolutionary track predicted
by a simple gas exhaustion model.
