Home About us Contact
|
Home About us Contact | ||
|
|
||
Dusty Tori (dusty + torus)
Selected AbstractsThe Granada workshop on High Redshift Radio Galaxies: An overviewASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006H. J. A. Röttgering Abstract The Granada workshop on High Redshift Radio Galaxies (HzRGs) gave an excellent overview of the progress that has been made in this field during the last 3 years. Here we briefly review some of the results, with an emphasis on what studies of HzRGs can teach us about the formation and evolution of massive galaxies, clusters and active galactic nuclei (AGN). Of great relevance for this workshop are scenarios that describe certain aspects of the evolution of radio galaxies, including (i) the sequence of events after merging of galaxies that ultimately lead to extended powerful radio sources and (ii) the mass assembly and virialization of the hosting massive galaxies and their associated (proto-)clusters. Furthermore, I briefly discuss two projects that are important for a further understanding of AGN and high redshift radio galaxies. First, using the MIDI instrument mounted on the VLT Interferometer, the dusty tori of nearby AGN can be studied in the range of 8,13 micron at high angular resolution. The first result on the nearby AGN NGC 1068 as presented by Jaffe et al. (2004) indicated the presence of a hot (T > 800 K), compact (,1 pc) component, possible identified with the base of the jet and a warm (270 K), well-resolved (3 × 4 pc) component associated with the alleged torus. Second, LOFAR is a new low frequency radio telescope that is currently being build in the Netherlands and is expected to be operational in 2008. With 50 stations spread over an area of 100 km in diameter, its resolution and sensitivity will be unprecedented in the frequency range 10,240 MHz. LOFAR will be a unique instrument that will impact a broad range of astrophysical topics varying from the epoch of reionisation, to gamma ray bursts and cosmic rays. Surveys with LOFAR will be of paramount importance for studies of HzRGs: It will enable (i) defining samples of radio galaxies with redshifts higher than 6, (ii) observations of starbursting galaxies in proto-clusters, and (iii) mapping out the low-frequency radio emission of virtually all northern radio-loud AGN in revolutionary detail. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radio galaxies and type-2 quasars in the Spitzer Extragalactic First Look SurveyASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006M. Lacy Abstract We use mid-infrared colour-colour plots made with data from the Spitzer First Look Survey to explore the emission mechanisms of faint radio sources in that field. Using mid-infrared colours alone, we are able to see the transition from a starburst-dominated radio source population at sub-mJy levels to the radiogalaxy/quasar population at mJy levels. Both FR I and some FR II galaxies show little or no mid-infrared excess, suggesting they either lack dusty tori, or a strong continuum source to heat them, or both. Objects with hot, dusty tori, most likely radio-intermediate and radio-quiet AGN, make up a significant fraction of the faint radio source population. We also discuss the use of mid-infrared colour-colour plots to select radio quiet obscured AGN. Early results from imaging the host galaxies of these type-2 quasars at high spatial resolution with adaptive optics indicates that they, like type-1 quasars and radio galaxies, are often found to be hosted by giant elliptical galaxies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Shock heating in the group atmosphere of the radio galaxy B2 0838+32AMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Nazirah N. Jetha ABSTRACT We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number 2.4+1.0,0.5 into the interstellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the active galactic nuclei (AGN) spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiatively inefficient accretion flow that could be controlled by an AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium. [source] A model for the infrared emission of FSC 10214+4724MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006Andreas Efstathiou ABSTRACT A model for the infrared emission of the high-redshift ultraluminous infrared galaxy FSC 10214+4724 is presented. The model assumes three components of emission: a dusty torus viewed edge-on, clouds that are associated with the narrow-line region and a highly obscured starburst. It is demonstrated that the presence of clouds in the narrow-line region, with a covering factor of 17 per cent, can explain why the mid-infrared spectrum of FSC 10214+4724 shows a silicate feature in emission despite the fact that its torus is viewed edge-on. It is also shown that the same model, but with the torus viewed face-on, predicts a spectrum with silicate emission features that is characteristic of the spectra of quasars recently observed with Spitzer. [source] | ||||||||||