Chandra high-energy grating observations of the Fe kα line core in type II Seyfert galaxies: a comparison with type I nuclei.
SHU X.W., YAQOOB T. and WANG J.X.
Abstract (from CDS):
We present a study of the core of the Fe Kα emission line at ∼6.4 keV in a sample of type II Seyfert galaxies observed by the Chandra high-energy grating. The sample consists of 29 observations of 10 unique sources. We present measurements of the Fe Kα line parameters with the highest spectral resolution currently available. In particular, we derive the most robust intrinsic line widths for some of the sources in the sample to date. We obtained a weighted mean full width at half-maximum (FWHM) of 2000±160 km/s for 8 out of 10 sources (the remaining sources had insufficient signal to noise). From a comparison with the optical emission-line widths obtained from spectropolarimetric observations, we found that the location of Fe Kα line-emitting material is a factor of ∼0.7-11 times the size of the optical broad-line region. Furthermore, compared to 13 type I active galactic nuclei (AGNs) for which the best Fe Kα line FWHM constraints were obtained, we found no difference in the FWHM distribution or the mean FWHM, and this conclusion is independent of the central black hole mass. This result suggests that the bulk of the Fe Kα line emission may originate from a universal region at the same radius with respect to the gravitational radius, ∼3x104 rg on average. By examining the correlation between the Fe Kα luminosity and the [O IV] line luminosity, we found a marginal difference in the Fe Kα line flux between type I and type II AGNs, but the spread in the ratio of LFe to L_[O IV]_is about two orders of magnitude. Our results confirm the theoretical expectation that the Fe Kα emission-line luminosity cannot trivially be used as a proxy of the intrinsic AGN luminosity, unless a detailed comparison of the data with proper models is applied.
galaxies: active - line: profiles - X-rays: galaxies