Catching Quenching Galaxies: The Nature of the WISE Infrared Transition
  Zone
  We present the discovery of a prominent bifurcation between early-type
galaxies and late-type galaxies, in [4.6]-[12] micron colors from the Wide
Field Infrared Survey Explorer (WISE). We then use an emission-line diagnostic
comparison sample to explore the nature of objects found both within, and near
the edges of, this WISE infrared transition zone (IRTZ). We hypothesize that
this birfurcation might be due to the presence of hot dust and PAH emission
features in late-type galaxies. Using a sample of galaxies selected through the
Shocked Poststarburst Galaxy Survey (SPOGS), we are able to identify galaxies
with strong Balmer absorption (EW(Hdelta)>5 Angstroms) as well as emission
lines inconsistent with star formation (deemed SPOG candidates, or SPOGs*) that
lie within the optical green valley. Seyferts and low ionization nuclear
emission line regions, whose u-r colors tend to be red, are strongly
represented within the IRTZ, whereas SPOGs* tend to sit near the star-forming
edge. Although AGN are well-represented in the IRTZ, we argue that the dominant
IRTZ population are galaxies that are in late stages of transitioning across
the optical green valley, shedding the last of their remnant interstellar
media.
