A Compton-thick AGN in the barred spiral galaxy NGC 4785
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 NH of at least 2 × 1024 cm-2 and absorption-corrected 2-10 keV X-ray power L2-10 ∼ few times 1042 erg s-1. Realistic uncertainties on L2-10 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2015
- DOI:
- 10.1093/mnras/stv344
- arXiv:
- arXiv:1408.4453
- Bibcode:
- 2015MNRAS.449.1845G
- Keywords:
-
- X-rays: individual: NGC 4785;
- X-rays: individual: NGC 4945;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 10 pages, 5 figures, 1 table, submitted