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M. Guainazzi F. Fiore G. Matt G.C. Perola 《Monthly notices of the Royal Astronomical Society》2001,327(1):323-328
We have studied the correlation among X-ray absorption, optical reddening and nuclear dust morphology in Seyfert 2 galaxies. Two main conclusions emerge: (i) the Balmer decrement and the amount of X-ray absorption are anticorrelated over a wide range of column density, – the correlation no longer applies to Compton-thick objects , although they span a comparable range in Balmer decrement; (ii) Compton-thin Seyfert 2s seem to prefer nuclear environments, which are rich in dust on scales of hundreds of parsecs. On the other hand, Compton-thick Seyferts indifferently exhibit 'dust-poor' and 'dust-rich' environments. These results support an extension of the Seyfert unification scenario (as recently proposed by Matt ), where Compton-thick Seyfert 2s are observed through compact 'torii', whereas Compton-thin ones are obscured by dust on much larger scales. 相似文献
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The host galaxies of active galactic nuclei 总被引:2,自引:0,他引:2
Guinevere Kauffmann Timothy M. Heckman Christy Tremonti Jarle Brinchmann Stéphane Charlot Simon D. M. White Susan E. Ridgway Jon Brinkmann Masataka Fukugita Patrick B. Hall eljko Ivezi Gordon T. Richards Donald P. Schneider 《Monthly notices of the Royal Astronomical Society》2003,346(4):1055-1077
We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with 0.02 < z < 0.3 selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O iii ] luminosities. 相似文献
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A high-velocity ionized outflow and XUV photosphere in the narrow emission line quasar PG1211+143 总被引:1,自引:0,他引:1
K. A. Pounds J. N. Reeves A. R. King K. L. Page P. T. O'Brien M. J. L. Turner 《Monthly notices of the Royal Astronomical Society》2003,345(3):705-713
We report on the analysis of a ∼60-ks XMM–Newton observation of the bright, narrow emission line quasar PG1211+143. Absorption lines are seen in both European Photon Imaging Camera and Reflection Grating Spectrometer spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionized outflow velocity of ∼24 000 km s−1 . The highest energy lines require a column density of N H ∼ 5 × 1023 cm−2 , at an ionization parameter of log ξ∼ 3.4 . If the origin of this high-velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius of ∼130 Schwarzschild radii, providing a natural explanation for the big blue bump (and strong soft X-ray) emission in PG1211+143. 相似文献
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C. S. Crawford A. C. Fabian P. Gandhi R. J. Wilman R. M. Johnstone 《Monthly notices of the Royal Astronomical Society》2001,324(2):427-442
We present observations of a sample of optically faint, hard X-ray sources of the kind likely to be responsible for much of the hard X-ray background. We confirm that such sources are easily detected in the near-infrared, and find that they have a featureless continuum suggesting that the active nucleus is heavily obscured. The infrared colours of the majority of the targets observed are consistent with absorbed elliptical host galaxies at z =1–2. It is likely that we are observing some of the brighter members of the important new class of X-ray type II quasars. 相似文献