595 research outputs found
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
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
Chandra Observation of the Cluster Environment of a WAT Radio Source in Abell 1446
Wide-angle tail (WAT) radio sources are often found in the centers of galaxy
clusters where intracluster medium (ICM) ram pressure may bend the lobes into
their characteristic C-shape. We examine the low redshift (z=0.1035) cluster
Abell 1446, host to the WAT radio source 1159+583. The cluster exhibits
possible evidence for a small-scale cluster-subcluster merger as a cause of the
WAT radio source morphology. This evidence includes the presence of temperature
and pressure substructure along the line that bisects the WAT as well as a
possible wake of stripped interstellar material or a disrupted cool core to the
southeast of the host galaxy. A filament to the north may represent cool,
infalling gas that's contributing to the WAT bending while spectroscopically
determined redshifts of member galaxies may indicate some component of a merger
occurring along the line-of-sight. The WAT model of high flow velocity and low
lobe density is examined as another scenario for the bending of 1159+583. It
has been argued that such a model would allow the ram pressure due to the
galaxy's slow motion through the ICM to shape the WAT source. A temperature
profile shows that the cluster is isothermal (kT= 4.0 keV) in a series of
annuli reaching a radius of 400 kpc. There is no evidence of an ongoing cooling
flow. Temperature, abundance, pressure, density, and mass profiles, as well as
two-dimensional maps of temperature and pressure are presented.Comment: 40 AASTeX pages including 15 postscript figures; accepted for
publication in Ap
Particle reacceleration in Coma cluster: radio properties and hard X-ray emission
The radio spectral index map of the Coma halo shows a progressive steepening
of the spectral index with increasing radius. Such a steepening cannot be
simply justified by models involving continuous injection of fresh particles in
the Coma halo or by models involving diffusion of fresh electrons from the
central regions. We propose a {\it two phase} model in which the relativistic
electrons injected in the Coma cluster by some processes (starbursts, AGNs,
shocks, turbulence) during a {\it first phase} in the past are systematically
reaccelerated during a {\it second phase} for a relatively long time ( 1
Gyr) up to the present time. We show that for reacceleration time scales of
Gyr this hypothesis can well account for the radio properties of
Coma C. For the same range of parameters which explain Coma C we have
calculated the expected fluxes from the inverse Compton scattering of the CMB
photons finding that the hard X-ray tail discovered by BeppoSAX may be
accounted for by the stronger reacceleration allowed by the model. The
possibility of extending the main model assumptions and findings to the case of
the other radio haloes is also discussed, the basic predictions being
consistent with the observations.Comment: 15 pages, 13 figures, accepted for publication in MNRA
A double radio halo in the close pair of galaxy clusters Abell 399 and Abell 401
Radio halos are faint radio sources usually located at the center of merging
clusters of galaxies. These diffuse radio sources are rare, having so far been
found only in about 30 clusters of galaxies, suggesting that particular
conditions are needed to form and maintain them. It is interesting to
investigate the presence of radio halos in close pairs of interacting clusters
in order to possibly clarify their origin in relation to the evolutionary state
of the merger. In this work, we study the case of the close pair of galaxy
clusters A399 and A401. A401 is already known to contain a faint radio halo,
while a hint of diffuse emission in A399 has been suggested based on the NVSS.
To confirm this possibility, we analyzed deeper Very Large Array observations
at 1.4 GHz of this cluster. We find that the central region of A399 is
permeated by a diffuse low-surface brightness radio emission that we classify
as a radio halo with a linear size of about 570 kpc and a central brightness of
0.3 micro-Jy/arcsec^2. Indeed, given their comparatively small projected
distance of about 3 Mpc, the pair of galaxy clusters A401 and A399 can be
considered as the first example of double radio halo system. The discovery of
this double halo is extraordinary given the rarity of these radio sources in
general and given that current X-ray data seem to suggest that the two clusters
are still in a pre-merger state. Therefore, the origin of the double radio halo
is likely to be attributed to the individual merging histories of each cluster
separately, rather than to the result of a close encounter between the two
systems.Comment: 6 pages, 4 figures, accepted for publication in A&
The Bologna Complete Sample of Nearby Radio Sources
We present a new, complete, sample of 95 radio sources selected from the B2
and 3CR catalogues, with z < 0.1. Since no selection effect on the core radio
power, jet velocity, or source orientation is present, this sample is well
suited for statistical studies. In this first paper we present the
observational status of all sources on the parsec (mas) and kiloparsec (arcsec)
scale; we give new parsec-scale data for 28 sources and discuss their
parsec-scale properties. Combining these data with those in the literature,
information on the parsec-scale morphology is available for a total of 53 radio
sources with different radio power and kpc-scale morphology. We investigate
their properties. We find a dramatically higher fraction of two-sided sources
in comparison to previous flux limited VLBI surveys.Comment: 29 pages, 21 figures - ApJ in press (10 Jan 2005 issue
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