808 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
The black hole mass of BL Lacs from stellar velocity dispersion of the host galaxy
We present the first results from our on-going program to estimate black hole
masses [M(BH)] of nearby BL Lac objects. The estimates are based on stellar
velocity dispersion (sigma) of the BL Lac host galaxies from optical
spectroscopy, and the recently found tight correlation between M{BH} and sigma
in nearby early-type galaxies. For the first three BL Lacs, we find log M(BH) =
7.5 - 8.7 and M(BH)/M(host) = 0.03 - 0.1.Comment: 2 pages, to appear in ESO Astrophysics Symposium "The Mass of
Galaxies at Low and High Redshift", eds. R. Bender & A. Renzin
Do local analogs of Lyman Break Galaxies exist?
The optical properties of a number of supercompact ultraviolet luminous
galaxies (UVLG), recently discovered in the local Universe matching GALEX and
Sloan Digital Sky Survey (SDSS) data, are discussed. Detailed re-analysis of
the SDSS data for these and other similar but nearer galaxies shows that their
surface brightness radial profile in both R and u bands is in most cases well
described by an extended disk plus a central unresolved component (possibly a
bulge). Since the SDSS pipeline used a single disk component to derive the half
light radius of these UVLGs their size was severely underestimated.
Consequently, the average UV surface brightness is much lower that previously
quoted casting doubts on the claim that UVLGs are the local analogs of high
redshift Lyman break galaxies.Comment: Accepted for publication on the Astrophysical Journal, 10 pages, 5
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