The Fastest Galaxy Evolution in an Unbiased Compact Group Sample with
  WISE
  We study the mid-infrared (MIR) properties of galaxies in compact groups and
their environmental dependence using the \textit{Wide-field Infrared Survey
Explorer (WISE)} data. We use a volume-limited sample of 670 compact groups and
their 2175 member galaxies with $M_r< -19.77$ and $0.01<z<0.0741$, drawn from
\citet{sohn+16}, which were identified using a friends-of-friends algorithm.
Among the 2175 galaxies, 1541 galaxies are detected at \textit{WISE} 12
$\micron$ with a signal-to-noise ratio greater than 3. Among the 1541 galaxies,
433 AGN-host galaxies are identified by using both optical and MIR
classification scheme. Using the remaining 1108 non-AGN galaxies, we find that
the MIR $[3.4]-[12]$ colors of compact group early-type galaxies are on average
bluer than those of cluster early-type galaxies. When compact groups have both
early- and late-type member galaxies, the MIR colors of the late-type members
in those compact groups are bluer than the MIR colors of cluster late-type
galaxies. As compact groups are located in denser regions, they tend to have
larger early-type galaxy fractions and bluer MIR color galaxies. These trends
are also seen for neighboring galaxies around compact groups. However, compact
group member galaxies always have larger early-type galaxy fractions and bluer
MIR colors than their neighboring galaxies. Our findings suggest that the
properties of compact group galaxies depend on both internal and external
environments of compact groups, and that galaxy evolution is faster in compact
groups than in the central regions of clusters.
