Study of Swift/BAT selected low-luminosity active galactic nuclei observed with Suzaku

Journal Article · Tue Nov 01 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/831/1/37· OSTI ID:22868549

Kawamuro, Taiki; Ueda, Yoshihiro ^[1]; Tazaki, Fumie ^[2]; Terashima, Yuichi ^[3]; Mushotzky, Richard ^[4]

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1. Department of Astronomy, Kyoto University, Kyoto 606-8502 (Japan)
2. Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan)
3. Department of Physics, Ehime University, Matsuyama 790-8577 (Japan)
4. Department of Astronomy, University of Maryland, CollegePark, MD 20742-2421 (United States)

We systematically analyze the broadband (0.5–200 keV) X-ray spectra of hard X-ray (>10 keV) selected local low-luminosity active galactic nuclei (LLAGNs) observed with Suzaku and Swift/BAT. The sample consists of 10 LLAGNs detected with Swift/BAT with intrinsic 14–195 keV luminosities smaller than 10{sup 42} erg s{sup −1} available in the Suzaku archive, covering a wide range of the Eddington ratio from 10{sup −5} to 10{sup −2}. The overall spectra can be reproduced with an absorbed cut-off power law, often accompanied by reflection components from distant cold matter, and/or optically thin thermal emission from the host galaxy. In all of the objects, relativistic reflection components from the innermost disk are not required. Eight objects show a significant narrow iron-Kα emission line. Comparing their observed equivalent widths with the predictions from the Monte-Carlo-based torus model by Ikeda et al. (2009), we constrain the column density in the equatorial plane to be log N{sub H}{sup eq}>22.7, or the torus half-opening angle θ {sub oa} < 70°. We infer that the Eddington ratio (λ {sub Edd}) is a key parameter that determines the torus structure of LLAGNs: the torus becomes large at λ {sub Edd} ≳ 2 × 10{sup −4}, whereas at lower accretion rates it is little developed. The luminosity correlation between the hard X-ray and mid-infrared (MIR) bands of the LLAGNs follows the same correlation as for more luminous AGNs. This implies that mechanisms other than AGN-heated dust are responsible for the MIR emission in low Eddington ratio LLAGNs.

• OSTI ID: 22868549
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 831; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
CORRELATIONS
COSMIC DUST
DENSITY
EMISSION
FORECASTING
GALAXY NUCLEI
HARD X RADIATION
IRON
KEV RANGE
LUMINOSITY
MONTE CARLO METHOD
REFLECTION
RELATIVISTIC RANGE
X-RAY GALAXIES
X-RAY SPECTRA