AEGIS: The Morphologies of Green Galaxies at 0.4<z<1.2
  We present quantitative morphologies of ~300 galaxies in the
optically-defined green valley at 0.4<z<1.2, in order to constrain the
mechanism(s) responsible for quenching star formation in the bulk of this
population. The sample is selected from galaxies in the All-Wavelength Extended
Groth Strip International Survey (AEGIS). While the green valley is defined
using optical U-B colors, we find that using a green valley sample defined
using NUV-R colors does not change the results. Using HST/ACS imaging, we study
several quantitative morphological parameters including CAS, B/T from GIM2D,
and Gini/M_20. We find that the green galaxy population is intermediate between
the red and blue galaxy populations in terms of concentration, asymmetry, and
morphological type and merger fraction estimated using Gini/M_20. We find that
most green galaxies are not classified as mergers; in fact, the merger fraction
in the green valley is lower than in the blue cloud. We show that at a given
stellar mass, green galaxies have higher concentration values than blue
galaxies and lower concentration values than red galaxies. Additionally, we
find that 12% of green galaxies have B/T = 0 and 21% with B/T \leq 0.05. Our
results show that green galaxies are generally massive (M\ast ~ 10^10.5 M_sun)
disk galaxies with high concentrations. We conclude that major mergers are
likely not the sole mechanism responsible for quenching star formation in this
population and that either other external processes or internal secular
processes play an important role both in driving gas towards the center of
these galaxies and in quenching star formation.
