8,864 research outputs found
Tailed radio galaxies as tracers of galaxy clusters. Serendipitous discoveries with the GMRT
We report on the discovery of four new radio galaxies with tailed morphology.
Tailed radio galaxies are generally found in rich environments, therefore their
presence can be used as tracer of a cluster. The radio galaxies were found in
the fields of Giant Metrewave Radio Telescope (GMRT) observations carried out
at 610 MHz and 327 MHz devoted to other studies. We inspected the literature
and archives in the optical and X-ray bands to search for galaxy clusters or
groups hosting them. All the tailed radio galaxies serendipitously found in the
GMRT fields are located in rich environments. Two of them belong to the
candidate cluster NCS J090232+204358, located at z(phot)=0.0746; one belongs to
the cluster MaxBCGJ223.97317+22.15620 at z(phot)=0.2619; finally we suggest
that the fourth one is probing a galaxy cluster at z=0.1177, located behind
A262, and so far undetected in any band. Our results strenghten the relevance
of high sensitivity and high resolution radio data in the detection of galaxy
clusters at intermediate redshift.Comment: 8 pages, accepted for publication on Astronomy & Astrophysic
The cluster relic source in A521
We present high sensitivity radio observations of the merging cluster A521,
at a mean redsfhit z=0.247. The observations were carried out with the GMRT at
610 MHz and cover a region of 1 square degree, with a sensitivity limit
of = 35 Jy b. The most relevant result of these
observations is the presence of a radio relic at the cluster periphery, at the
edge of a region where group infalling into the main cluster is taking place.
Thanks to the wealth of information available in the literature in the optical
and X-ray bands, a multi--band study of the relic and its surroundings was
performed. Our analysis is suggestive of a connection between this source and
the complex ongoing merger in the A521 region. The relic might be ``revived'
fossil radio plasma through adiabatic compression of the magnetic field or
shock re--acceleration due to the merger events. We also briefly discussed the
possibility that this source is the result of induced ram pressure stripping of
radio lobes associated with the nearby cluster radio galaxy J0454--1016a.
Allowing for the large uncertainties due to the small statistics, the number of
radio emitting early--type galaxies found in A521 is consistent with the
expectations from the standard radio luminosity function for local (z0.09)
cluster ellipticals.Comment: 30 pages 8 figures, 5 tables, accepted by New Astronom
High sensitivity low frequency radio observations of cD galaxies
We present the GMRT 235 MHz images of three radio galaxies and 610 MHz images
of two sources belonging to a complete sample of cD galaxies in rich and poor
galaxy clusters. The analysis of the spectral properties confirms the presence
of aged radio emission in two of the presented sources.Comment: 3 pages, 2 figures, To appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Radio Properties of the Shapley Concentration. III. Merging Clusters in the A3558 Complex
We present the results of a 22 cm radio survey carried out with the A3558
complex, a chain formed by the merging ACO clusters A3556-A3558-A3562 and
thetwo groups SC1327-312 and SC1323-313, located in the central region of the
complex, a chain formed by the merging ACO clusters A3556-A3558-A3562 and the
two groups SC1327-312 and SC1323-313, located in the central region of the
Shapley Concentration. The purpose of our survey is to study the effects of
cluster mergers on the statistical properties of radio galaxies and to
investigate the connection between mergers and the presence of radio halos and
relic sources. We found that the radio source counts in the A3558 complex are
consistent with the background source counts. Furthermore, we found that no
correlation exists between the local density and the radio source power, and
that steep spectrum radio galaxies are not segregated in denser optical
regions. The radio luminosity function for elliptical and S0 galaxies is
significantly lower than that for cluster type galaxies and for those not
selected to be in clusters at radio powers logP(1.4) > 22.5, implying that the
probability of a galaxy becoming a radio source above this power limit is lower
in the Shapley Concentration compared with any other environment. The detection
of a head-tail source in the centre of A3562, coupled with careful inspection
of the 20 cm NRAO VLA Sky Survey (NVSS) and of 36 cm MOST observations, allowed
us to spot two extended sources in the region between A3562 and SC1329-313,
i.e. a candidate radio halo at the centre of A3562, and low brightness extended
emission around a 14.96 magnitude Shapley galaxy.Comment: 18 pages, 14 figures. Accepted for publication on MNRA
Radio emission at the centre of the galaxy cluster Abell 3560: evidence for core sloshing?
Previous radio observations of the galaxy cluster A3560 in the Shapley
Concentration showed complex radio emission associated with the brightest
cluster member.To understand its origin we observed it with the GMRT, the VLA
and ATCA at 240 and 610 MHz, 1.28,1.4, 2.3,4.8 and 8.4 GHz, and performed a
detailed morphological and spectral study of the radio emission associated with
the BCG. We also observed the cluster with XMM-Newton and Chandra to derive the
properties of the ICM. The radio emission of the N-E nucleus of the dumb-bell
BCG shows an active radio galaxy, plus aged diffuse emission, which is not
refurbished at present. Our Chandra data show that the radio active nucleus of
the BCG has extended X-ray emission, which we classify as a low-luminosity
corona. A residual image of the XMM-Newton brightness shows the presence of a
spiral-like feature, which we interpret as the signature of gas sloshing. The
presence of a subgroup is clear in the surface brightness residual map, and in
the XMM-Newton temperature analysis. The optical 2D analysis shows substructure
in A3560. A galaxy clump was found at the location of the X-ray subgroup, and
another group is present south of the cluster core, close to the spiral-like
feature. The aged part of the radio emission closely follows the spiral pattern
of the X-ray residual brightness distribution, while the two active radio lobes
are bent in a completely different direction. We conclude that the complex
radio emission associated with the cluster BCG is the result of a minor merger
event in A3560. The aged diffuse emission is strongly affected by the sloshing
motion in the ICM. On the other hand, the bent jets and lobes of the current
radio AGN activity may reflect a complex gas velocity field in the innermost
cluster regions and/or sloshing-induced oscillations in the motion of the cD
galaxy.Comment: 15 pages, 8 figures, 5 tables, A&A in pres
Radio halos in merging clusters of galaxies
We present the preliminary results of 235 MHz, 327 MHz and 610 MHz
observations of the galaxy cluster A3562 in the core of the Shapley
Concentration. The purpose of these observations, carried out with the Giant
Metrewave Radio Telescope (GMRT, Pune, India) was to study the radio halo
located at the centre of A3562 and determine the shape of its radio spectrum at
low frequencies, in order to understand the origin of this source. In the
framework of the re--acceleration model, the preliminary analysis of the halo
spectrum suggests that we are observing a young source (few yrs) at the
beginning of the re--acceleration phase.Comment: 3 pages, 2 figures. Proceedings of IAU Colloquium 195 - Outskirts of
Galaxy Clusters: intense life in the suburb
GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4. II.The eBCS clusters and analysis of the complete sample
We present the results of the GMRT cluster radio halo survey. The main
purposes of our observational project are to measure which fraction of massive
galaxy clusters in the redshift range z=0.2--0.4 hosts a radio halo, and to
constrain the expectations of the particle re--acceleration model for the
origin of the non--thermal radio emission. We selected a complete sample of 50
clusters in the X-ray band from the REFLEX (27) and the eBCS (23) catalogues.
In this paper we present Giant Metrewave Radio Telescope (GMRT) observations at
610 MHz for all clusters still lacking high sensitivity radio information, i.e.
16 eBCS and 7 REFLEX clusters, thus completing the radio information for the
whole sample. The typical sensitivity in our images is in the range 1Jy b. We found a radio halo in A697, a diffuse
peripheral source of unclear nature in A781, a core--halo source in Z7160, a
candidate radio halo in A1682 and ``suspect'' central emission in Z2661.
Including the literature information, a total of 10 clusters in the sample host
a radio halo. A very important result of our work is that 25 out of the 34
clusters observed with the GMRT do not host extended central emission at the
sensitivity level of our observations, and for 20 of them firm upper limits to
the radio power of a giant radio halo were derived. The GMRT Radio Halo Survey
shows that radio halos are not common, and our findings on the fraction of
giant radio halos in massive clusters are consistent with the statistical
expectations based on the re--acceleration model. Our results favour primary to
secondary electron models.Comment: A&A in press, 17 pages, 12 figures, 4 tables Version with high
quality figures available on web at
http://www.ira.inaf.it/~tventuri/pap/Venturi_web.pd
Reconstruction of Scalar Potentials in Modified Gravity Models
We employ the superpotential technique for the reconstruction of cosmological
models with a non-minimally coupled scalar field evolving on a spatially flat
Friedmann-Robertson-Walker background. The key point in this method is that the
Hubble parameter is considered as a function of the scalar field and this
allows one to reconstruct the scalar field potential and determine the dynamics
of the field itself, without a priori fixing the Hubble parameter as a function
of time or of the scale factor. The scalar field potentials that lead to de
Sitter or asymptotic de Sitter solutions, and those that reproduce the
cosmological evolution given by Einstein-Hilbert action plus a barotropic
perfect fluid, have been obtained.Comment: 12 pages, 2 figures, accepted for publication in PR
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