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|XMM-Newton spectra of hard spectrum Rosat AGN: X-ray absorption and optical reddening|
We present the XMM-Newton spectra of three low-redshift intermediateSeyferts (one Sy 1.5, and two Sy 1.8), from our survey of hard spectrumRosat sources. The three AGN are well fitted by absorbed powerlaws, withintrinsic nuclear photoelectric absorption from column densities between1.3 and 4.0 × 1021 cm-2. In the brightestobject the X-ray spectrum is good enough to show that the absorber isnot significantly ionized. For all three objects the powerlaw slopesappear to be somewhat flatter (Γ1.3-1.6) than those found intypical unabsorbed Seyferts. The constraints from optical and X-rayemission lines imply that all three objects are Compton-thin. For thetwo fainter objects, the reddening deduced from the optical broademission lines in one of them, and the optical continuum in the other,are similar to those expected from the X-ray absorption, if we assume aGalactic gas-to-dust ratio and reddening curve. The broad line regionBalmer decrement of our brightest object is larger than expected fromits X-ray absorption, which can be explained either by an intrinsicBalmer decrement with standard gas-to-dust ratio, or by a >Galacticgas-to-dust ratio. These Galactic ratios of extinction to photoelectricabsorption cannot extend to the high redshift, high luminosity, broadline AGN in our sample, because they have column densities>1022 cm-2, and so their broad line regionswould be totally obscured. This means that some effect (e.g., luminositydependence, or evolution) needs to be present in order to explain thewhole population of absorbed AGN.
|A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources|
We have surveyed 188 ROSAT Position Sensitive Proportional Counter(PSPC) fields for X-ray sources with hard spectra (α<0.5) suchsources must be major contributors to the X-ray background at faintfluxes. In this paper we present optical identifications for 62 of thesesources: 28 active galactic nuclei (AGN) which show broad lines in theiroptical spectra (BLAGN), 13 narrow emission line galaxies (NELGs), fivegalaxies with no visible emission lines, eight clusters and eightGalactic stars. The BLAGN, NELGs and galaxies have similar distributionsof X-ray flux and spectra. Their ROSAT spectra are consistent with theirbeing AGN obscured by columns of20.51)identified hard sources have broad lines.
|A survey of hard spectrum ROSAT sources - I. X-ray source catalogue|
We present a catalogue of 147 serendipitous X-ray sources selected tohave hard spectra (α<0.5) from a survey of 188 ROSAT fields.Such sources must be the dominant contributors to the X-ray backgroundat faint fluxes. We have used Monte Carlo simulations to verify that ourtechnique is very efficient at selecting hard sources: the survey has>=10 times as much effective area for hard sources as it has for softsources above a 0.5-2keV flux level of10-14ergcm-2s-1. The distribution ofbest-fitting spectral slopes of the hard sources suggests that a typicalROSAT hard source in our survey has a spectral slope α~0. The hardsources have a steep number flux relation (dN/dS~S-γwith a best-fitting value of γ=2.72+/-0.12) and make up about15per cent of all 0.5-2keV sources withS>10-14ergcm-2s-1. If their N(S)continues to fainter fluxes, the hard sources will comprise ~40per centof sources with5×10-15
|The Luminosity Function of Elliptical Galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1032M&db_key=AST
|Associations between quasi-stellar objects and galaxies|
A table is presented here listing all close pairs of QSOs and galaxiesthat were found in a computer-aided search of catalogs of QSOs andbright galaxies and an extensive search of the literature. There is alarge excess of pairs with separations of 2 arcmin lor less, or about 60kpc, over the numbers expected if the configurations were accidental.The angular separation for 392 pairs adds to the evidence for physicalassociation, and it is shown that selection effects are not important. Ageneral rule is stated that QSOs tend to lie in the vicinity of normalgalaxies much more often than is expected by chance whether or not thegalaxies and the QSOs have the same redshifts. It is emphasized thatthis rule cannot be explained in terms of gravitational microlensing,and it is concluded that some part of the redshift of all classes ofactive nuclei is not associated with the expansion of the universe.
|Southern Galaxy Catalogue.|
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