LIFTING THE VEIL ON OBSCURED ACCRETION: ACTIVE GALACTIC NUCLEI NUMBER COUNTS AND SURVEY STRATEGIES FOR IMAGING HARD X-RAY MISSIONS

Journal Article · Wed Jul 20 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/736/1/56· OSTI ID:21578299

Ballantyne, D R; Draper, A R ^[1]; Madsen, K K ^[2]; Rigby, J R ^[3]; Treister, E ^[4]

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1. Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States)
2. Space Radiation Laboratory, California Institute of Technology, MC: 220-47, Pasadena, CA 91125 (United States)
3. Carnegie Observatories, Carnegie Institution of Washington, Pasadena, CA 91101 (United States)
4. Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

Finding and characterizing the population of active galactic nuclei (AGNs) that produces the X-ray background (XRB) is necessary to connect the history of accretion to observations of galaxy evolution at longer wavelengths. The year 2012 will see the deployment of the first hard X-ray imaging telescope which, through deep extragalactic surveys, will be able to measure the AGN population at the energies where the XRB peaks ({approx}20-30 keV). Here, we present predictions of AGN number counts in three hard X-ray bandpasses: 6-10 keV, 10-30 keV, and 30-60 keV. Separate predictions are presented for the number counts of Compton thick AGNs, the most heavily obscured active galaxies. The number counts are calculated for five different models of the XRB that differ in the assumed hard X-ray luminosity function, the evolution of the Compton thick AGNs, and the underlying AGN spectral model. The majority of the hard X-ray number counts will be Compton thin AGNs, but there is a greater than tenfold increase in the Compton thick number counts from the 6-10 keV to the 10-30 keV band. The Compton thick population shows enough variation that a hard X-ray number counts measurement will constrain the models. The computed number counts are used to consider various survey strategies for the NuSTAR mission, assuming a total exposure time of 6.2 Ms. We find that multiple surveys will allow a measurement of Compton thick evolution. The predictions presented here should be useful for all future imaging hard X-ray missions.

• OSTI ID: 21578299
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 736; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELECTROMAGNETIC RADIATION
EVOLUTION
GALACTIC EVOLUTION
GALAXY NUCLEI
HARD X RADIATION
IONIZING RADIATIONS
RADIATIONS
X RADIATION