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The Soft X-Ray Properties of Nearby Low-Luminosity Active Galactic Nuclei and their Contribution to the Cosmic X-Ray Background
We have examined ROSAT soft X-ray observations of a complete,distance-limited sample of Seyfert and LINER galaxies. X-ray data areavailable for 46 out of 60 such objects which lie within a hemisphere ofradius 18 Mpc. We have constructed radial profiles of the nuclearsources in order to characterize their spatial extent and, in somecases, to help constrain the amount of flux associated with a nuclearpoint source. PSPC data from ROSAT have been used to explore thespectral characteristics of the objects with sufficient numbers ofdetected counts. Based on the typical spectral parameters of thesesources, we have estimated the luminosities of the weaker sources in thesample. We then explore the relationship between the soft X-ray andHα luminosities of the observed objects; these quantities arecorrelated for higher luminosity AGNs. We find a weak correlation at lowluminosities as well, and we have used this relationship to predictLX for the 14 objects in our sample that lack X-ray data.Using the results of the spatial and spectral analyses, we have comparedthe X-ray properties of Seyferts and LINERs, finding no strikingdifferences between the two classes of objects. However, both types ofobjects often exhibit significant amounts of extended emission, whichcould minimize the appearance of differences in their nuclearproperties. The soft X-ray characteristics of the type 1 and type 2active galaxies in the sample are also discussed. We then compute thelocal X-ray volume emissivity of low-luminosity Seyferts and LINERs andinvestigate their contribution to the cosmic X-ray background. The0.5-2.0 keV volume emissivity of 2.2×1038 ergss-1 Mpc-3 we obtain for our sample suggests thatlow-luminosity AGNs produce at least 9% of the soft X-ray background.
| Accurate Positions for MCG Galaxies
We have measured accurate celestial coordinates for 4741 extragalacticobjects, primarily drawn from a list of MCG galaxies with no recentlypublished accurate positions. The standard deviations in the newpositions depend slightly on the measurement method but are on the orderof 1.0" to 1.2". Standard deviations in the original MCG positions areconfirmed to be at the 1.5′-2.0′ level. These new positionswere integrated into NED in 1997 December.
| Atlas of interacting galaxies, Part. II and the concept of fragmentation of galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...28....1V&db_key=AST
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