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Astron. Astrophys. 341, 683-692 (1999)

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High-resolution imaging of Einstein Slew Survey BL Lacertae objects *

J. Heidt 1, K. Nilsson 2, A. Sillanpää 2, L.O. Takalo 2 and T. Pursimo 2

1 Landessternwarte Heidelberg, Königstuhl, D-69117 Heidelberg, Germany
2 Tuorla Observatory, FIN-21500 Piikkiö, Finland

Received 2 June 1998 / Accepted 29 October 1998


High-resolution images of 7 newly identified BL Lac objects (among them one BL Lac candidate) at z [FORMULA] 0.2 from the Einstein Slew Survey are presented for the first time. In all cases we were able to resolve the host galaxy. Our 2-dimensional analysis of the host galaxies shows that all these BL Lac objects are embedded in elliptical galaxies with an average [FORMULA] = -23.1 and [FORMULA] = 10 kpc. One BL Lac might have both a bulge and an underlying disk. These results are similar to those obtained for the hosts of other BL Lac objects.

We searched in our BL Lac objects for host galaxies, whose surface brightness distribution does not follow a pure de Vaucouleurs law and determined the statistical significance with numerical simulations. In two BL Lac objects (1ES 1255+244 and 1ES 1959+650) significant deviations were found.

The environments of the BL Lac objects are highly interesting. In at least two (perhaps three) cases we found evidence for interaction. All BL Lac objects (except one) have at least 2 companions, some of which are bright, within a projected distance of 60 kpc from the BL Lac. In two cases we found 5 companions within 50 kpc. This implies that gravitational interaction is potentially important to the BL Lac phenomenon at least in these sources.

Key words: methods: data analysis – galaxies: active – galaxies: BL Lacertae objects: general – galaxies: elliptical and lenticular, cD – galaxies: interactions

* Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma, jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Institute de Astrofisica de Canarias.

Send offprint requests to: J. Heidt (jheidt@lsw.uni-heidelberg.de)

© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998