Accretion-Inhibited Star Formation in the Warm Molecular Disk of the
  Green-valley Elliptical Galaxy NGC 3226
  We present archival Spitzer photometry and spectroscopy, and Herschel
photometry, of the peculiar "Green Valley" elliptical galaxy NGC~3226. The
galaxy, which contains a low-luminosity AGN, forms a pair with NGC~3227, and is
shown to lie in a complex web of stellar and HI filaments. Imaging at 8 and
16$\mu$m reveals a curved plume structure 3 kpc in extent, embedded within the
core of the galaxy, and coincident with the termination of a 30 kpc-long HI
tail. In-situ star formation associated with the IR plume is identified from
narrow-band HST imaging. The end of the IR-plume coincides with a warm
molecular hydrogen disk and dusty ring, containing 0.7-1.1 $\times$ 10$^7$
M$_{\odot}$ detected within the central kpc. Sensitive upper limits to the
detection of cold molecular gas may indicate that a large fraction of the H$_2$
is in a warm state. Photometry, derived from the UV to the far-IR, shows
evidence for a low star formation rate of $\sim$0.04 M$_{\odot}$ yr$^{-1}$
averaged over the last 100 Myrs. A mid-IR component to the Spectral Energy
Distribution (SED) contributes $\sim$20$\%$ of the IR luminosity of the galaxy,
and is consistent with emission associated with the AGN. The current measured
star formation rate is insufficient to explain NGC3226's global UV-optical
"green" colors via the resurgence of star formation in a "red and dead" galaxy.
This form of "cold accretion" from a tidal stream would appear to be an
inefficient way to rejuvenate early-type galaxies, and may actually inhibit
star formation.
