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Astron. Astrophys. 323, 739-748 (1997)


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Radio-loud active galaxies in the northern ROSAT All-Sky Survey

II. Multi-frequency properties of unidentified sources *

W. Brinkmann 1, J. Siebert 1, E.D. Feigelson 2, R.I. Kollgaard 2, S.A. Laurent-Muehleisen 2, W. Reich 3, E. Fürst 3, P. Reich 3, W. Voges 1, J. Trümper 1 and R. McMahon 4

1 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching, Germany
2 Dept. of Astronomy & Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
4 Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK

Received 6 August 1996 / Accepted 14 January 1997

Abstract

We present the broad band, radio - to - X-ray, properties of a large sample of mostly previously optically unidentified radio-loud X-ray sources from the correlation of a ROSAT All-Sky Survey source list with the 5 GHz Green Bank Survey of the northern sky (RGB sample) which is one of the largest well-defined flux-limited surveys of AGN ever obtained. Further, the RGB pushes 1-2 orders of magnitude deeper in both X-ray and radio flux compared to previous unbiased wide-area AGN surveys.

Follow up VLA observations of the candidate objects yielded positions with arcsec accuracy which were used to find optical counterparts to the sources from digitized POSS plates. The sources are divided into three classes according to the positional offset between the X-ray and radio candidates and the spatial resolution of the radio observations, reflecting the various degrees of confidence about the correctness of the proposed association.

Although the nature of the sources as well as their redshifts remain to be determined in spectroscopic follow up observations, the derived flux ratios lead to the conclusion that the majority of them are quasars. Hardly any correlations could be found between different source parameters, possibly due to the fact that most of the objects are found in a relatively small flux range near the sensitivity limit of the radio catalogue.

The majority of the new RGB sources have broad-band properties between those of traditional radio-selected and X-ray selected AGN. There is no bimodal distribution in the radio-loudness distribution, and the traditional division between radio-quiet and radio-loud AGN may not be warranted

Key words: galaxies: active – quasars; X-rays: general – radio sources: general

* Tables 1-4 are available in electronic form at the CDS via anonymous ftp 130.79.128.5

Send offprint requests to: W. Brinkmann

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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