Studying Faint Ultra Hard X-ray Emission from AGN in GOALS LIRGs with
  Swift BAT
  We present the first analysis of the all-sky Swift BAT ultra hard X-ray
(14-195 keV) data for a targeted list of objects. We find the BAT data can be
studied at 3x fainter limits than in previous blind detection catalogs based on
prior knowledge of source positions and using smaller energy ranges for source
detection. We determine the AGN fraction in 134 nearby (z<0.05) luminous
infrared galaxies (LIRGS) from the GOALS sample. We find that LIRGs have a
higher detection frequency than galaxies matched in stellar mass and redshift
at 14-195 keV and 24-35 keV. In agreement with work at other wavelengths, the
AGN detection fraction increases strongly at high IR luminosity with half of
high luminosity LIRGs (50%, 6/12, log L_IR/L_sun>11.8) detected. The BAT AGN
classification shows 97% (37/38) agreement with Chandra and XMM AGN
classification using hardness ratios or detection of a iron K-alpha line. This
confirms our statistical analysis and supports the use of the Swift BAT all-sky
survey to study fainter populations of any category of sources in the ultra
hard X-ray band. BAT AGN in LIRGs tend to show higher column densities with
40\pm9% showing 14-195 keV/2-10 keV hardness flux ratios suggestive of high or
Compton-thick column densities (log N_H>24 cm^-2), compared to only 12\pm5% of
non-LIRG BAT AGN. We also find that using specific energy ranges of the BAT
detector can yield additional sources over total band detections with 24%
(5/21) of detections in LIRGs at 24-35 keV not detected at 14-195 keV.
