395 research outputs found
The nature of close companions of the BL Lac Objects 1ES 0502+675 and 1ES 1440+122
We report on deep radio images and optical spectroscopy of two BL Lac objects
that have very close compact companions. The two targets, 1ES 0502+675 and 1ES
1440+122, were selected from the HST imaging survey of 110 BL Lacs as
candidates for possible gravitational lensing. The new observations clearly
demonstrate that the companion objects are not secondary images of the active
nuclei but, in spite of the relatively low chance projection probability,
foreground Galactic stars. Gravitational lensing appears to be unimportant to
the BL Lac phenomenon. We discuss the radio properties of the BL Lac objects in
the context of standard beaming models, and show they are as expected for
beamed FRI radio galaxies.Comment: 13 pages, 5 figures, ApJ in pres
Blue colours of BL Lac host galaxies
Near-infrared and optical imaging of BL Lac host galaxies is used to
investigate their colour properties. We find that the R-H colour and colour
gradient distributions of the BL Lac hosts are much wider than those for normal
ellipticals, and many objects have very blue hosts and/or steep colour
gradients. The blue colours are most likely caused by recent star formation.
The lack of obvious signs of interaction may, however, require a significant
time delay between the interaction event with associated star formation
episodes and the onset of the nuclear activity.Comment: 2 pages, 1 figure, to appear in the proceedings of "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. T.
Storchi Bergmann, L.C. Ho, and H.R. Schmit
Optical surface photometry of radio galaxies - II. Observations and data analysis
Optical imaging observations for 50 radio galaxies are presented. For each
object isophotal contours, photometric profiles, structural parameters
(position angle, ellipticity, Fourier coefficients), and total magnitudes are
given. These observations, obtained in the Cousins R band, complement the data
presented in a previous paper and are part of a larger project aimed at
studying the optical properties of low redshift (z<0.12) radio galaxies (Govoni
et al. 1999). Comments for each individual source are reported.Comment: 9 pages, plus 17 .gif figures, accepted by Astronomy and
Astrophysics, Supplement Serie
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