Infrared and Hard X-Ray Diagnostics of Active Galactic Nucleus Identification from the Swift/BAT and AKARI All-sky Surveys
Abstract
We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (>10 keV) properties for local active galactic nuclei (AGNs). The Swift Burst Alert Telescope all-sky survey provides an unbiased, flux-limited selection of hard X-ray-detected AGNs. Cross-correlating the 22 month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGNs detected by the AKARI instruments. We find a strong correlation for most AGNs between the infrared (9, 18, and 90 μm) and hard X-ray (14-195 keV) luminosities, and quantify the correlation for various subsamples of AGNs. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1 galaxies, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick (CT) sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity versus infrared color diagram, in which type 1 radio-loud AGNs are well isolated from the others in the sample. The other uses the X-ray versus infrared color as a useful redshift-independent indicator for identifying CT AGNs. Importantly, CT AGNs and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2012
- DOI:
- 10.1088/0004-637X/753/2/104
- arXiv:
- arXiv:1205.0140
- Bibcode:
- 2012ApJ...753..104M
- Keywords:
-
- galaxies: active;
- infrared: galaxies;
- X-rays: galaxies;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 17 pages, 5 figures, 5 tables. Accepted for publication in the Astrophysical Journal