Studying faint ultra-hard X-ray emission from AGN in GOALS LIRGs with Swift/BAT.
KOSS M., MUSHOTZKY R., BAUMGARTNER W., VEILLEUX S., TUELLER J., MARKWARDT C. and CASEY C.M.
Abstract (from CDS):
We present the first analysis of the all-sky Swift Burst Alert Telescope (BAT) ultra-hard X-ray (14-195 keV) data for a targeted list of objects. We find that the BAT data can be studied at three-times-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 active galactic nucleus (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 the high-luminosity LIRGs (50%, 6/12, log LIR/L☉> 11.8) detected. The BAT AGN classification shows 97% (37/38) agreement with Chandra and XMM-Newton AGN classification using hardness ratios or detection of an iron Kα 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 AGNs in LIRGs tend to show higher column densities with 40%±9% showing 14-195 keV/2-10 keV hardness flux ratios suggestive of high or Compton-thick column densities (log NH> 24/cm2), compared to only 12%±5% of non-LIRG BAT AGNs. 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.
galaxies: active - X-rays: galaxies
VizieR on-line data:
<Available at CDS (J/ApJ/765/L26): table1.dat>