* Astronomy

Blobrana · L

RE: NGC 3783

Blobrana · L

Dusty black holes could affect galaxy growth, scientists say

New evidence showing that black holes eject dusty matter from their surroundings, potentially affecting the growth of galaxies, has been revealed by an international team of scientists.
The researchers used a powerful telescope - with enough resolution to read a road sign in New York from London - to view the black hole at the centre of an active spiral galaxy 150 million light years from Earth.
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Blobrana · L

Fuel for the black hole

First investigations of a galactic nucleus with the AMBER instrument of the Very Large Telescope Interferometer in Chile

An international research team led by Gerd Weigelt from the Max-Planck-Institut für Radioastronomie in Bonn reports on high-resolution studies of an active galactic nucleus in the near-infrared. The observations were carried out with the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO). The use of near-infrared interferometry allowed the team to resolve a ring-shaped dust distribution (generally called "dust torus") in the inner region of the nucleus of the active galaxy NGC 3783. This dust torus probably represents the reservoir of gaseous and dusty material that "feeds" the hot gas disk ("accretion disk") and the supermassive black hole in the centre of this galaxy. The resolved dust torus has an angular radius of only 0.7 milli-arcseconds on the sky, an angle that is 5 million times smaller than one degree. This angular radius corresponds to a radius of approximately 0.5 light years for a distance of 150 million light years. Studies of the physical properties of these dust tori are very important to improve our understanding of their structure and interaction with the accretion disk. To obtain these measurements, the light from up to three telescopes of the Very Large Telescope Interferometer was interferometrically combined. This method is able to achieve an angular resolution equivalent to the resolution of a telescope with a diameter of 130 Metres.
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Blobrana · L

Title: A Monte Carlo Markov Chain based investigation of black hole spin in the active galaxy NGC3783
Authors: C.S.Reynolds, L.W.Brenneman, A.M.Lohfink, M.L.Trippe, J.M.Miller, A.C.Fabian, M.A.Nowak

The analysis of relativistically broadened X-ray spectral features from the inner accretion disk provides a powerful tool for measuring the spin of supermassive black holes (SMBH) in active galactic nuclei (AGN). However, AGN spectra are often complex and careful analysis employing appropriate and self-consistent models are required if one is to obtain robust results. In this paper, we revisit the deep July-2009 Suzaku observation of the Seyfert galaxy NGC3783 in order to study in a rigorous manner the robustness of the inferred black hole spin parameter. Using Monte Carlo Markov Chain (MCMC) techniques, we identify a (partial) modelling degeneracy between the iron abundance of the disk and the black hole spin parameter. We show that the data for NGC3783 strongly require both supersolar iron abundance (Z_Fe=2-4Zsun) and a rapidly spinning black hole (a>0.88). We discuss various astrophysical considerations that can affect the measured abundance. We note that, while the abundance enhancement inferred in NGC3783 is modest, the X-ray analysis of some other objects has found extreme iron abundances. We introduce the hypothesis that the radiative levitation of iron ions in the innermost regions of radiation-dominated AGN disks can enhance the photospheric abundance of iron. We show that radiative levitation is a plausible mechanism in the very inner regions of high accretion rate AGN disks.

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Blobrana · L

Title: The Spin of the Supermassive Black Hole in NGC 3783
Authors: L.W. Brenneman, C.S. Reynolds, M.A. Nowak, R.C. Reis, M. Trippe, A.C. Fabian, K. Iwasawa, J.C. Lee, J.M. Miller, R.F. Mushotzky, K. Nandra, M. Volonteri

The Suzaku AGN Spin Survey is designed to determine the supermassive black hole spin in six nearby active galactic nuclei (AGN) via deep Suzaku stares, thereby giving us our first glimpse of the local black hole spin distribution. Here, we present an analysis of the first target to be studied under the auspices of this Key Project, the Seyfert galaxy NGC 3783. Despite complexity in the spectrum arising from a multi-component warm absorber, we detect and study relativistic reflection from the inner accretion disk. Assuming that the X-ray reflection is from the surface of a flat disk around a Kerr black hole, and that no X-ray reflection occurs within the general relativistic radius of marginal stability, we determine a lower limit on the black hole spin of a > 0.88 (99% confidence). We examine the robustness of this result to the assumption of the analysis, and present a brief discussion of spin-related selection biases that might affect flux-limited samples of AGN.

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