3,603 research outputs found
B2 1144+35B, a giant low power radio galaxy with superluminal motion. Orientation and evidence for recurrent activity
The goal of this work is a detailed study of the nearby, low power radio
galaxy B2 1144+35B. For this purpose, we performed new Very Long Baseline Array
(VLBA) and Very Large Array (VLA) observations. This source has several
properties (bright, nearby, large range of spatial structures, visible
counterjet, etc.) that make it an excellent astrophysical laboratory for the
study of the evolution of radio jets. Here we report the detection of motion in
the counterjet at 0.23 0.07 c, which allows us to estimate the
orientation of the parsec-scale jet at 33 from the line of
sight, with an intrinsic velocity of (0.94)c. We also report
on a brightening of the core at high frequencies which we suggest could be the
result of a new component emerging from the core. High dynamic range VLBA
observations at 5 GHz reveal, for the first time, extended emission connecting
the core with the bright complex of emission that dominates the flux density of
the parsec scale structure at frequencies below 20 GHz. The evolution of this
bright complex is considered and its slow decline in flux density is
interpreted as the result of an interaction with the interstellar medium of the
host galaxy.Comment: 7 pages, 6 b&w figures. A&A in pres
VLBI observations of nearby radio loud Active Galactic Nuclei
We present an update of the parsec scale properties of the Bologna Complete
Sample consisting of 95 radio sources from the B2 Catalog of Radio Sources and
the Third Cambridge Revised Catalog (3CR), with z < 0.1. Thanks to recent new
data we have now parsec scale images for 76 sources of the sample. Most of them
show a one-sided jet structure but we find a higher fraction of two-sided
sources in comparison with previous flux-limited VLBI surveys. A few peculiar
sources are presented and discussed in more detail.Comment: 6 pages, 7 figures, Proceedings for "The Universe under the
Microscope" (AHAR 2008), April 2008, to be published in Journal of Physics:
Conference Series by Institute of Physics Publishing; R. Schoedel, A. Eckart,
S. Pfalzner, and E. Ros ed
Halo and Relic Sources in Clusters of Galaxies
New images of 7 radio halos and relics, obtained with the Very Large Array at
20 or 90 cm, are presented here. The existence of a cluster-wide radio halo in
the clusters A 665 and CL 0016+16 is confirmed. Both these clusters share the
properties of the other clusters with radio halos, i.e. are luminous in X-rays,
have high temperature, and show recent merger processes. No diffuse sources are
detected in a sample of clusters showing at least a tailed radio galaxy within
300 kpc from the cluster center, indicating that the connection between tailed
radio galaxies and halos is not relevant. For these clusters we give limits to
the surface brightness and to the angular size of possible undetected diffuse
sources.Comment: 16 Figures in separated files. A large ps file with figures
(gg-aug00.ps.gz) in the text is avaialble at
ftp://terra.bo.cnr.it/papers/journals New Astronomy Vol. 5, p.335, in pres
A sample of low-redshift BL Lacertae objects. II. EVN and MERLIN data and multi-wavelength analysis
We present new radio observations of 9 members of a sample of 29 nearby (z <
0.2) BL Lac objects. The new data have been obtained with the European VLBI
Network and/or the MERLIN at 1.6 and 5 GHz and complement previous
observations. For one object, the TeV source Mrk 421, we also present deep
multi-epoch VLBA and Global VLBI data, which reveal a resolved diffuse jet,
with clear signatures of limb brightening. We use the new and old data to
estimate physical parameters of the jets of the sample from which the subset
with new radio data is drawn. We derive Doppler factors in the parsec scale
radio jet in the range ~2 < delta < ~9. Using HST data, we separate the
contribution of the host galaxy from that of the active core. From the measured
and de-beamed observables, we find a weak correlation between radio power and
black hole mass, and a tight correlation between radio and optical core
luminosities. We interpret this result in terms of a common synchrotron origin,
with little contribution from a radiatively efficient accretion disk. The BL
Lacs in our sample have de-beamed properties similar to low power radio
galaxies, including the fundamental plane of black hole activity.Comment: Accepted by ApJ. 17 page
Radio Halo and Relic Candidates from the NRAO VLA Sky Survey
We present the first results of the search of new halo and relic candidates
in the NRAO VLA Sky Survey. We have inspected a sample of 205 clusters from the
X-ray-brightest Abell-type clusters presented by Ebeling et al (1996), and
found 29 candidates. Out of them, 11 clusters are already known from the
literature to contain a diffuse cluster-wide source, while in 18 clusters this
is the first indication of the existence of this type of sources. We classify
these sources as halos or relics according to their location in the cluster
center or periphery, respectively. We find that the occurrence of cluster halos
and relics is higher in clusters with high X-ray luminosity and high
temperature. We also confirm the correlation between the absence of a cooling
flow and the presence of a radio halo at the cluster center.Comment: 25 Pages, 4 Figures included in the text, Figures 3a to 3g in
separated files. New Astronomy in pres
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