Issue |
Astron. Astrophys. Suppl. Ser.
Volume 134, Number 2, January II 1999
|
|
---|---|---|
Page(s) | 221 - 240 | |
DOI | https://doi.org/10.1051/aas:1999136 | |
Published online | 15 January 1999 |
Radio-loud ROSAT sources near the North Ecliptic Pole
1
Max-Planck Institut für extraterrestrische Physik, P.O. Box 1603, D-85740 Garching, Germany
2
Dept. of Physics, Bucknell University, Lewisburg, PA 17837, U.S.A.
3
Fermi National Accelerator Laboratory, Batavia, IL 60510, U.S.A.
4
Dept. of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, U.S.A.
5
E.O. Hulburt Center for Space Research, Naval Research Laboratory, Washington DC 20375-5320, U.S.A.
Send offprint request to: W. Brinkmann
Received:
6
March
1998
Accepted:
6
August
1998
A deep and large-area survey of the North Ecliptic Pole region was made
with the ROSAT All-Sky Survey and the VLA to elucidate
the population of radio-loud extragalactic objects. A region of 29.3 square
degrees was surveyed with sensitivities around erg s-1
cm-2 in the soft X-ray band and 1 mJy at 1.5 GHz. Optical
counterparts were sought on digitized Schmidt plates from POSS-I and
II. Seventy-four reliable RASS-VLA sources were found.
The sample is a heterogeneous mixture of Seyfert galaxies, quasars, BL
Lac objects, galaxy clusters and groups containing a radio galaxy.
Optical magnitudes range from
to
. Three
results are noteworthy: (1) the bimodality in the ratio of radio to
optical emission seen in optically- and X-ray-selected AGN samples is
also evident in the ROSAT-VLA objects; (2) X-ray and radio selection
is an effective method for locating poor galaxy clusters and groups;
and (3) a considerable population of optically faint but
X-ray/radio-bright objects is present. This last group may be either
distant clusters with radio galaxies or "red quasars".
Key words: galaxies: active / clusters: general / quasars: general / X–rays: general / radio continuum: galaxies
© European Southern Observatory (ESO), 1999