A Compton-thick AGN in the barred spiral galaxy NGC 4785
Date Issued
2015
Author(s)
Gandhi, P.
•
Yamada, S.
•
Ricci, C.
•
Asmus, D.
•
Mushotzky, R. F.
•
Ueda, Y.
•
Terashima, Y.
•
Abstract
We present X-ray observations of the active galactic nucleus (AGN) in NGC 4785. The source is a local Seyfert 2 which has not been studied so far in much detail. It was recently detected with high significance in the 15-60 keV band in the 66-month Swift/BAT (Burst Array Telescope) all sky survey, but there have been no prior pointed X-ray observations of this object. With Suzaku, we clearly detect the source below 10 keV, and find it to have a flat continuum and prominent neutral iron fluorescence line with equivalent width ≳1 keV. Fitting the broad-band spectra with physical reflection models shows the source to be a Compton-thick AGN with N_H of at least 2 × 10^24 cm^-2 and absorption-corrected 2-10 keV X-ray power L_2-10 ∼ few times 10^42 erg s^-1. Realistic uncertainties on L_2-10 computed from the joint confidence interval on the intrinsic power-law continuum photon index and normalization are at least a factor of 10. The local bona fide Compton-thick AGN population is highly heterogeneous in terms of WISE mid-infrared source colours, and the nucleus of NGC 4785 appears especially sub-dominant in the mid-infrared when comparing to other Compton-thick AGN. Such sources would not be easily found using mid-infrared selection alone. The extent of host galaxy extinction to the nucleus is not clear, though NGC 4785 shows a complex core with a double bar and inner disc, adding to the list of known Compton-thick AGN in barred host galaxies.
Volume
449
Issue
2
Start page
1845
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.449.1845G
Rights
open.access
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