  Supernova (SN) rates serve as an important probe of star-formation models and
initial mass functions. Near-infrared seeing-limited ground-based surveys
typically discover a factor of 3-10 fewer SNe than predicted from far-infrared
(FIR) luminosities owing to sensitivity limitations arising from both a
variable point-spread function (PSF) and high dust extinction in the nuclear
regions of star-forming galaxies. This inconsistency has potential implications
for our understanding of star-formation rates and massive-star evolution,
particularly at higher redshifts, where star-forming galaxies are more common.
To resolve this inconsistency, a successful SN survey in the local universe
must be conducted at longer wavelengths and with a space-based telescope, which
has a stable PSF to reduce the necessity for any subtraction algorithms and
thus residuals. Here we report on a two-year Spitzer/IRAC 3.6 um survey for
dust-extinguished SNe in the nuclear regions of forty luminous infrared
galaxies (LIRGs) within 200 Mpc. The asymmetric Spitzer PSF results in worse
than expected subtraction residuals when implementing standard template
subtraction. Forward-modeling techniques improve our sensitivity by ~1.5
magnitudes. We report the detection of 9 SNe, five of which were not discovered
by optical surveys. After adjusting our predicted rates to account for the
sensitivity of our survey, we find that the number of detections is consistent
with the models. While this search is nonetheless hampered by a
difficult-to-model PSF and the relatively poor resolution of Spitzer, it will
benefit from future missions, such as Roman Space Telescope and JWST, with
higher resolution and more symmetric PSFs.
