A Compton-thick AGN in the barred spiral galaxy NGC 4785

作者：Gandhi P^*; Yamada S; Ricci C; Asmus D; Mushotzky R F; Ueda Y; Terashima Y; La Parola V

来源：Monthly Notices of the Royal Astronomical Society, 2015, 449(2): 1845-1855.

DOI：10.1093/mnras/stv344

• X-rays: individual: NGC 4785
• X-rays: individual: NGC 4945

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 greater than or similar to 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 x 10(24) cm(-2) and absorption-corrected 2-10 keV X-ray power L2-10 similar to few times 10(42) 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.

• 出版日期2015-5-11