The Local Cluster Survey I: Evidence of Outside-In Quenching in Dense
  Environments
  The goal of the Local Cluster Survey is to look for evidence of
environmentally driven quenching among star-forming galaxies in nearby galaxy
groups and clusters. Quenching is linked with environment and stellar mass, and
much of the current observational evidence comes from the integrated properties
of galaxies. However, the relative size of the stellar and star-forming disk is
sensitive to environmental processing and can help identify the mechanisms that
lead to a large fraction of quenched galaxies in dense environments. Toward
this end, we measure the size of the star-forming disks for 224 galaxies in
nine groups and clusters (0.02<z<0.04; SFR > 0.1 M$_\odot$/yr) using 24um
imaging from the Spitzer Space Telescope. We normalize the 24um effective
radius (R24) by the size of the stellar disk (Rd). We find that star-forming
galaxies with higher bulge-to-total ratios (B/T) and galaxies in more dense
environments have more centrally concentrated star formation. Comparison with
H~I mass fractions and NUV-r colors indicates that a galaxy's transition from
gas-rich and blue to depleted and red is accompanied by an increase in the
central concentration of star formation. We build a simple model to constrain
the timescale over which the star-forming disks shrink in the cluster
environment. Our results are consistent with a long-timescale (>2Gyr) mechanism
that produces outside-in quenching, such as the removal of the extended gas
halo or weak stripping of the cold disk gas.
