7,070 research outputs found
Optical surface photometry of radio galaxies - II. Observations and data analysis
Optical imaging observations for 50 radio galaxies are presented. For each
object isophotal contours, photometric profiles, structural parameters
(position angle, ellipticity, Fourier coefficients), and total magnitudes are
given. These observations, obtained in the Cousins R band, complement the data
presented in a previous paper and are part of a larger project aimed at
studying the optical properties of low redshift (z<0.12) radio galaxies (Govoni
et al. 1999). Comments for each individual source are reported.Comment: 9 pages, plus 17 .gif figures, accepted by Astronomy and
Astrophysics, Supplement Serie
The intracluster magnetic field power spectrum in Abell 2382
The goal of this work is to put constraints on the strength and structure of
the magnetic field in the cluster of galaxies A2382. We investigate the
relationship between magnetic field and Faraday rotation effects in the
cluster, using numerical simulations as a reference for the observed
polarization properties. For this purpose we present Very Large Array
observations at 20 cm and 6 cm of two polarized radio sources embedded in
A2382, and we obtained detailed rotation measure images for both of them. We
simulated random three-dimensional magnetic field models with different power
spectra and thus produced synthetic rotation measure images. By comparing our
simulations with the observed polarization properties of the radio sources, we
can determine the strength and the power spectrum of intra-cluster magnetic
field fluctuations that best reproduce the observations. The data are
consistent with a power law magnetic field power spectrum with the Kolmogorov
index , while the outer scale of the magnetic field fluctuations is of
the order of 35 kpc. The average magnetic field strength at the cluster center
is about 3 G and decreases in the external region as the square root of
the electron gas density. The average magnetic field strength in the central 1
Mpc is about 1 G.Comment: Comments: 18 pages, 13 figures, accepted by A&A. For a version with
high quality figures, see http://erg.ca.astro.it/preprints/guidetti2007
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
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
Cell Ultrastructure in Disease
The doctor of today must adopt the \u27cellular way of thinking\u27 in the evaluation of diseases. This ultrastructural outlook provides him with much indispensable information that also serves a practical purpose. A diseased cell organelle is at the basis of every clinical sign and any attempt of therapy must be aimed at that specific point of lesion. We intend, in the light of a long experience, to propose to clinicians a new way of thinking in which a precise correlation between symptoms and sub-microscopic changes of the cell is considered. Many different examples amply justify this proposal. Electron microscopy can contribute by enabling a) identification of structural sub-cellular modifications suitable for the finest differential diagnosis, b) more and more complete understanding of pathogenic pathways of various diseases, c) the establishment of guidelines for precise pharmacological interventions at the molecular level
Structure of the magnetoionic medium around the FR Class I radio galaxy 3C 449
The goal of this work is to constrain the strength and structure of the
magnetic field associated with the environment of the radio source 3C 449,
using observations of Faraday rotation, which we model with a structure
function technique and by comparison with numerical simulations. We assume that
the magnetic field is a Gaussian, isotropic random variable and that it is
embedded in the hot intra-group plasma surrounding the radio source. For this
purpose, we present detailed rotation measure images for the polarized radio
source 3C 449, previously observed with the Very Large Array at seven
frequencies between 1.365 and 8.385 GHz. We quantify the statistics of the
magnetic-field fluctuations by deriving rotation measure structure functions,
which we fit using models derived from theoretical power spectra. We quantify
the errors due to sampling by making multiple two-dimensional realizations of
the best-fitting power spectrum.We also use depolarization measurements to
estimate the minimum scale of the field variations. We then make
three-dimensional models with a gas density distribution derived from X-ray
observations and a random magnetic field with this power spectrum. Under these
assumptions we find that both rotation measure and depolarization data are
consistent with a broken power-law magnetic-field power spectrum, with a break
at about 11 kpc and slopes of 2.98 and 2.07 at smaller and larger scales
respectively. The maximum and minimum scales of the fluctuations are around 65
and 0.2 kpc, respectively. The average magnetic field strength at the cluster
centre is 3.5 +/-1.2 micro-G, decreasing linearly with the gas density within
about 16 kpc of the nucleus.Comment: 19 pages; 14 figures; accepted for publication on A&A. For a high
quality version use ftp://ftp.eso.org/pub/general/guidetti
Detection of diffuse radio emission in the galaxy clusters A800, A910, A1550, and CL1446+26
Radio halos are elusive sources located at the center of merging galaxy
clusters. To date, only about 40 radio halos are known, thus the discovery of
new halos provide important insights on this class of sources. To improve the
statistics of radio halos, we investigated the radio continuum emission in a
sample of galaxy clusters. We analyzed archival Very Large Array observations
at 1.4 GHz, with a resolution of about 1 arcmin. These observations
complemented by X-ray, optical, and higher resolution radio data allowed to
detect a new radio halo in the central region of A800 and A1550. We discovered
a radio relic in the periphery of A910, and finally we revealed both a halo and
a relic in CL1446+26.Clusters hosting these new halos show an offset between
the radio and the X-ray peak. By analyzing this offset statistically we found
that radio halos can be quite asymmetric with respect to the X-ray gas
distribution, with an average radio - X-ray displacement of about 180 kpc. When
the offsets are normalized by the halo size, there is a tendency for smaller
halos to show larger displacements.Comment: Accepted by Astronomy and Astrophysics, 13 pages, 8 figure
Testing the radio halo-cluster merger scenario. The case of RXCJ2003.5-2323
We present a combined radio, X-ray and optical study of the galaxy cluster
RXCJ2003.5-2323. The cluster hosts one of the largest, most powerful and
distant giant radio halos known to date, suggesting that it may be undergoing a
strong merger process. The aim of our multiwavelength study is to investigate
the radio-halo cluster merger scenario. We studied the radio properties of the
giant radio halo in RXCJ2003.5-2323 by means of new radio data obtained at 1.4
GHz with the Very Large Array, and at 240 MHz with the Giant Metrewave Radio
Telescope, in combination with previously published GMRT data at 610 MHz. The
dynamical state of the cluster was investigated by means of X-ray Chandra
observations and optical ESO--NTT observations. Our study confirms that
RXCJ2003.5-2323 is an unrelaxed cluster. The unusual filamentary and clumpy
morphology of the radio halo could be due to a combination of the filamentary
structure of the magnetic field and turbulence in the inital stage of a cluster
merger.Comment: 10 page, 10 figures, accepted for publication on A&
An elusive radio halo in the merging cluster Abell 781?
Deep radio observations of the galaxy cluster Abell 781 have been carried out
using the Giant Metrewave Radio Telescope at 325 MHz and have been compared to
previous 610 MHz observations and to archival VLA 1.4 GHz data. The radio
emission from the cluster is dominated by a diffuse source located at the
outskirts of the X-ray emission, which we tentatively classify as a radio
relic. We detected residual diffuse emission at the cluster centre at the level
of S(325 MHz)~15-20 mJy. Our analysis disagrees with Govoni et al. (2011), and
on the basis of simple spectral considerations we do not support their claim of
a radio halo with flux density of 20-30 mJy at 1.4 GHz. Abell 781, a massive
and merging cluster, is an intriguing case. Assuming that the residual emission
is indicative of the presence of a radio halo barely detectable at our
sensitivity level, it could be a very steep spectrum source.Comment: 5 pages, 4 figures, 1 table - Accepted for publication on Monthly
Notices of the Royal Astronomical Society Letter
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