X-ray obscuration and obscured AGN in the local universe
Abstract
We discuss the X-ray properties of 49 local (z<0.035) Seyfert 2 galaxies with HST/WFC2 high-resolution optical coverage. It includes the results of 26 still unpublished Chandra and XMM-Newton observations, which yield 25 (22) new X-ray detections in the 0.5-2 keV (2-10 keV) energy band. Our sample covers a range in the 2-10 keV observed flux, F2-10, from 3 × 10-11 to 6 × 10-15 erg cm-2 s-1. The percentage of objects that are likely obscured by Compton-thick matter (column density, NH ≥ σt-1 ≃ 1.6 × 1024 cm-2) is ≃50%, and reaches ≃80% for log (F2-10) < 12.3. Hence, Kα fluorescent iron lines with large Equivalent Width ({EW} > 0.6 keV) are common in our sample (6 new detections at a confidence level ≥2σ). They are explained as due to reflection off the illuminated side of optically thick material. We confirm a correlation between the presence of a 100-pc scale nuclear dust in the WFC2 images and Compton-thin obscuration. We interpret this correlation as due to the large covering fraction of gas associated with the dust lanes. The X-ray spectra of highly obscured AGN invariably present a prominent soft excess emission above the extrapolation of the hard X-ray component. This soft component can account for a very large fraction of the overall X-ray energy budget. As this component is generally unobscured - and therefore likely produced in extended gas structures - it may lead to a severe underestimation of the nuclear obscuration in z ∼ 1 absorbed AGN, if standard X-ray colors are used to classify them. As a by-product of our study, we report the discovery of a soft X-ray, luminous (≃7 × 1040 erg s-1) halo embedding the interacting galaxy pair Mkn 266.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2005
- DOI:
- 10.1051/0004-6361:20053643
- arXiv:
- arXiv:astro-ph/0508265
- Bibcode:
- 2005A&A...444..119G
- Keywords:
-
- galaxies: active;
- galaxies: nucleus;
- galaxies: Seyfert;
- X-ray: galaxies;
- Astrophysics
- E-Print:
- 16 pages, 12 figures, To appear in Astronomy &