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Abstract: The ROSAT ALL Sky Survey Bright Source Catalogue RASS-BSC has beencorrelated with the Catalogue of Principal Galaxies PGC to identify newextragalactic counterparts. 550 reliable optical counterparts have beendetected. We took optical spectra of 176 X-ray candidates and companions atESO, Calar Alto observatory and McDonald observatory. We discuss the redshift-,linewidth-, as well as optical and X-ray luminosity distribution of our ROSATselected sample. 139 galaxies of our 166 X-ray counterparts have beenidentified as AGN with 93 being Seyfert 1 galaxies 61%. Eighteen of them20% are Narrow Line Seyfert 1 galaxies. 34 X-ray candidates 21% are LINERsand only eight candidates 5% are Seyfert 2. The ratio of the number ofSeyfert 1 galaxies to Seyfert 2 galaxies is about 11-1. Optical surveys resultin ratios of 1-1.4. The high fraction of detected Seyfert 1 galaxies isexplained by the sensitivity of the ROSAT to soft X-rays which are heavilyabsorbed in type 2 AGN. Two X-ray candidates are HII-galaxies and 25 candidates15% show no signs of spectral activity. The AGN in our RASS selected sampleexhibit slightly higher optical luminosities M B = -20.71 +- 1.75 mag andsimilar X-ray luminosities logL X erg-s = 42.9 +- 1.7 compared to otherAGN surveys. The Halpha line width distribution FWHM of our newly identifiedROSAT AGN sample is similar to the line widths distribution based on SDSS AGN.However, our newly identified RASS AGN have rather reddish colors explainingwhy they have not been detected before in ultraviolet or blue excess surveys.



Autor: W. Kollatschny, R. Kotulla, W. Pietsch, K. Bischoff, M. Zetzl

Fuente: https://arxiv.org/







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