The ROSAT Bright Survey:
I. Identification of an AGN sample with hard ROSAT X-ray spectra
Astron. Nachr.,
in press
Contact: aschwope@aip.de
Preprint of paper
(10.5 Mb gzip'ed postscript)
J.-U. Fischer [1], G. Hasinger [1], A.D. Schwope [1], H. Brunner [1],
Th. Boller [2], J. Trümper [2], W. Voges [2], S. Neizvestny [3]
- Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
- Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
- Special Astrophysical Observatory, Nizhnij Arkhyz, Russia
Abstract
The ROSAT Bright Survey (RBS) aims to completely optically identify the more
than 2000 brightest sources detected in the ROSAT all-sky survey at galactic
latitudes |b| > 30 degr (excluding LMC, SMC, Virgo cluster).
This paper presents a subsample of 66 bright point-like ROSAT survey
sources with almost hard PSPC spectra, the hardness ratio HR1 is > 0.5 for
most of the sources. The subsample
could be nearly completely identified
by low-resolution optical spectroscopy with the following
breakdown into object classes: 31
Seyfert galaxies, 22 BL Lac candidates,
5 clusters of galaxies, 1 cataclysmic variable, and 5 bright stars.
Only one object remained unidentified and one X-ray source was a spurious
detection.
The redshift distribution peaks around 0.06 for the Seyferts and around 0.13
for the BL Lac candidates.
Observations with medium spectral resolution were obtained for most
of the new Seyfert galaxies.
A large fraction (20 objects) are type 1 Seyfert galaxies,
the other fraction includes Seyfert galaxies of type 1.5 - 1.8 (5 objects),
two LINERs, and 4 possible narrow-line Seyfert 1 galaxies (NLS1).
About one third of the new Seyfert's have nearby companion galaxies
displaying either emission or absorption lines at the same redshift.
Among them are a couple of systems showing
direct morphological evidence for interaction.
The large fraction of interacting galaxies among our sample
suggests a scenario where interaction is the main trigger of AGN activity.