1,959 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&
Cosmic rays in magnetized intracluster plasma
Recent results are reported on Magnetic Fields in Clusters of Galaxies,
Diffuse Radio Emission, and Radio - X-ray connection in Radio Halos.Comment: 2 pages, 1 figure, Invited talk at the JD15 "Magnetic Fields in
Diffuse Media", IAU XXVII General Assembly, Rio de Janeir
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
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
The intracluster magnetic field power spectrum in Abell 665
The goal of this work is to investigate the power spectrum of the magnetic
field associated with the giant radio halo in the galaxy cluster A665. For
this, we present new deep Very Large Array total intensity and polarization
observations at 1.4 GHz. We simulated Gaussian random three-dimensional
turbulent magnetic field models to reproduce the observed radio halo emission.
By comparing observed and synthetic radio halo images we constrained the
strength and structure of the intracluster magnetic field. We assumed that the
magnetic field power spectrum is a power law with a Kolmogorov index and we
imposed a local equipartition of energy density between relativistic particles
and field. Under these assumptions, we find that the radio halo emission in
A665 is consistent with a central magnetic field strength of about 1.3 micro-G.
To explain the azimuthally averaged radio brightness profile, the magnetic
field energy density should decrease following the thermal gas density, leading
to an averaged magnetic field strength over the central 1 Mpc^3 of about 0.75
micro-G. From the observed brightness fluctuations of the radio halo, we infer
that the outer scale of the magnetic field power spectrum is ~450 kpc, and the
corresponding magnetic field auto-correlation length is ~100 kpc.Comment: 12 pages, 6 figures, accepted for publication on A&A, language
editing. For a high quality version see
http://erg.ca.astro.it/preprints/a665_halo
Magnetic Fields and Faraday Rotation in Clusters of Galaxies
We present a numerical approach to investigate the relationship between
magnetic fields and Faraday rotation effects in clusters of galaxies. We can
infer the structure and strength of intra-cluster magnetic fields by comparing
our simulations with the observed polarization properties of extended cluster
radio sources such as radio galaxies and halos. We find the observations
require a magnetic field which fluctuates over a wide range of spatial scales
(at least one order of magnitude). If several polarized radio sources are
located at different projected positions in a galaxy cluster, as is the case
for A119, detailed Faraday rotation images allow us to constrain both the
magnetic field strength and the slope of the power spectrum. Our results show
that the standard analytic expressions applied in the literature overestimate
the cluster magnetic field strengths by a factor of about 2. We investigate the
possible effects of our models on beam depolarization of radio sources whose
radiation traverses the magnetized intracluster medium. Finally, we point out
that radio halos may provide important information about the spatial power
spectrum of the magnetic field fluctuations on large scales. In particular,
different values of the index of the power spectrum produce very different
total intensity and polarization brightness distributions.Comment: 19 pages, 11 figures. Accepted for publication in A&
Dental pathology in present-day and copper age samples
Dental paleopathology has become an excellent
discipline to reconstruct the oral health of ancient
populations and its trend from the past to the present
day, especially regarding dietary habits. Our preliminary
research aims to perform a comparative analysis on
dental health status of two widely chronologically
distant samples from Sardinia: the first one dates back
to the Copper Age (III mill. B.C.) and comes from a
collective hypogean burial named Scabâe Arriu (Siddi,
SU), the second one is composed by extracted teeth
of present-day individuals, collected during some
traineeships at the Department of Surgical Science of
the Dentistry School, in Cagliari
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