427 research outputs found
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 giant radio halo in Abell 2163
New radio data is presented for the rich cluster Abell 2163. The cluster
radio emission is characterized by the presence of a radio halo, which is one
of the most powerful and extended halos known so far. In the NE peripheral
cluster region, we also detect diffuse elongated emission, which we classify as
a cluster relic. The cluster A2163 is very hot and luminous in X-ray. Its
central region is probably in a highly non relaxed state, suggesting that this
cluster is likely to be a recent merger. The existence of a radio halo in this
cluster confirms that halos are associated with hot massive clusters, and
confirms the connection between radio halos and cluster merger processes. The
comparison between the radio emission of the halo and the cluster X-ray
emission shows a close structural similarity. A power law correlation is found
between the radio and X-ray brightness, with index = 0.64. We also report the
upper limit to the hard X-ray emission, obtained from a BeppoSAX observation.
We discuss the implications of our results.Comment: 7 pages, 8 figures (5 in ps and 3 in gif), Accepted for publication
in Astron. Astrop
Diffuse radio emission in a REFLEX cluster
Deep Very Large Array radio observations are presented for the REFLEX
clusters RXCJ0437.1+0043 and RXCJ1314.4-2515. They are at similar distance and
show similar X-ray luminosity, but they are quite different in X-ray structure.
Indeed RXCJ0437.1+0043 is regular and relaxed, whereas RXCJ1314.4-2515 is
characterized by substructure and possible merging processes. The radio images
reveal no diffuse emission in RXCJ0437.1+0043, and a complex diffuse structure
in RXCJ1314.4-2515. The diffuse source in the latter cluster consists of a
central radio halo which extends to the West toward the cluster periphery and
bends to the North to form a possible relic. Another extended source is
detected in the eastern cluster peripheral region. Although there could be
plausible optical identifications for this source, it might also be a relic
candidate owing to its very steep spectrum. The present results confirm the
tight link between diffuse cluster radio sources and cluster merger processes.Comment: Accepted for publication in A&A. Figures here have been degraded to
reduce their size. A version with full resolution figures is available at
http://www.ira.cnr.it/~lferetti/OUTGOING/papREFLEX.ps.g
New radio halos and relics in clusters of galaxies
We present here new images of relics and halo sources in rich cluster of
galaxies and the correlation between the halo radio surface brightness versus
the cluster bolometric X-ray luminosity.Comment: 2 pages, 4 figures. To appear in the Proceedings of the International
Conference: "The Origin and Evolution of Cosmic Magnetism"; Bologna 29 August
- 2 September 2005; eds R. Beck, G. Brunetti, L. Feretti, and B. Gaensler
(Astronomische Nachrichten, 2006
A Comparison of Radio and X-Ray Morphologies of Four Clusters of Galaxies Containing Radio Halos
Clusters of galaxies may contain cluster-wide, centrally located, diffuse
radio sources, called halos. They have been found to show morphologies similar
to those of the X-ray emission. To quantify this qualitative statement we
performed a point-to-point comparison of the radio and the X-ray emission for
four clusters of galaxies containing radio halos: Coma, Abell 2255, Abell 2319,
Abell 2744. Our study leads to a linear relation between the radio and the
X-ray surface brightness in two clusters, namely Abell 2255 and Abell 2744. In
Coma and A2319 the radio and the X-ray brightnesses seem to be related with a
sub-linear power law. Implications of these findings within simple radio halo
formation models are briefly discussed.Comment: 9 pages, 13 .ps figures, accepted by A&
Comparative analysis of the diffuse radio emission in the galaxy clusters A1835, A2029, and Ophiuchus
We recently performed a study of a sample of relaxed, cooling core galaxy
clusters with deep Very Large Array observations at 1.4 GHz. We find that in
the central regions of A1835, A2029, and Ophiuchus the dominant radio galaxy is
surrounded by a diffuse low-brightness radio emission that takes the form of a
mini-halo. Here we present the results of the analysis of the extended diffuse
radio emission in these mini-halos. In order to investigate the morphological
properties of the diffuse radio emission in clusters of galaxies we propose to
fit their azimuthally averaged brightness profile with an exponential,
obtaining the central brightness and the e-folding radius from which the radio
emissivity can be calculated. We investigate the radio properties of the
mini-halos in A1835, A2029, and Ophiuchus in comparison with the radio
properties of a representative sample of mini-halos and halos already known in
the literature. We find that radio halos can have quite different length-scales
but their emissivity is remarkably similar from one halo to the other. In
contrast, mini-halos span a wide range of radio emissivity. Some of them, like
the Perseus mini-halos, are characterized by a radio emissivity which is more
than 100 times greater than that of radio halos. On the other hand, the new
mini-halos in cooling core clusters analyzed in this work, namely A2029,
Ophiuchus, and A1835, have a radio emissivity which is much more typical of
halos in merging clusters rather than similar to that of the other mini-halos
previously known.Comment: 17 pages, 11 figures, A&A in press. For a version with high quality
figures, see http://erg.ca.astro.it/preprints/mini_halo_2
The nature of the giant diffuse non-thermal source in the A3411-A3412 complex
VLA deep radio images at 1.4 GHz in total intensity and polarization reveal a
diffuse non-thermal source in the interacting clusters A3411 - A3412. Moreover
a small-size low power radio halo at the center of the merging cluster A3411 is
found. We present here new optical and X-ray data and discuss the nature and
properties of the diffuse non-thermal source. We suggest that the giant diffuse
radio source is related to the presence of a large scale filamentary structure
and to multiple mergers in the A3411-A3412 complex.Comment: 7 pages, 6 figures, accepted for publication in MNRA
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