Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...268...53f&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 268, no. 1, p. 53-57.
Astronomy and Astrophysics
Astrophysics
25
Bl Lacertae Objects, Galactic Clusters, Radio Galaxies, Density Distribution, Red Shift, Relativistic Electron Beams
Scientific paper
We present direct imaging data of the fields of BL Lac objects drawn from the complete 1 Jy sample. An increase in galaxy surface density towards the BL Lac objects in subsamples with mean redshifts 0.28 and 0.65 is found. The covariance amplitudes 215 and 515 correspond roughly to galaxy clusters of richness classes 0 and 1, respectively. Similar covariance amplitudes have been found for radio galaxies; our result therefore can be naturally understood if the BL Lac phenomenon is due to relativistic beaming, i.e. the BL Lac objects are FRI radio galaxies with the jet pointing towards us. In contrast, a constant galaxy surface density is found for the subsample with mean redshift 0.97. This would also be expected under the beaming hypothesis, since cluster galaxies at z roughly 1 would be well below our detection limit. However, since at least in one case we find strong evidence for gravitational lensing, we suggest that the high redshift BL Lac objects are not a homogeneous class of objects, but rather contain both beamed and lensed objects.
Fried Josef W.
Kuehr Helmut
Stickel Manfred
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