1,714 research outputs found
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
Chemical Gradients in Galaxy Clusters and the Multiple Ways of Making a Cold Front
Cold fronts were originally interpreted as being the result of
subsonic/transonic motions of head-on merging substructures. This merger core
remnant model is theoretically justified and hold relatively well for clusters
that have clear signs of merging, such as 1E0657-56, but they do not work well
for the increasing number of cold fronts found in clusters that do not show
clear merging signs, such as A496. Here we report the results of a deeper
observation of that cluster that allowed us to produce high quality maps of the
gas parameters and to compare more closely the observations with the
predictions given by different models for cold front formation. We found for
the first time a ``cold arm'' characteristic of a flyby of a massive DM halo
near the core of the cluster. The cold arm is accompanied by an enhanced SN II
Fe mass fraction, inconsistent with the merger core remnant scenario.Comment: 3 pages, 1 figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Temperature Structure of the Intra-Cluster Medium from SPH and AMR simulations
Analyses of cosmological hydrodynamic simulations of galaxy clusters suggest
that X-ray masses can be underestimated by 10% to 30%. The largest bias
originates by both violation of hydrostatic equilibrium and an additional
temperature bias caused by inhomogeneities in the X-ray emitting intra-cluster
medium (ICM). To elucidate on this large dispersion among theoretical
predictions, we evaluate the degree of temperature structures in cluster sets
simulated either with smoothed-particle-hydrodynamics (SPH) and
adaptive-mesh-refinement (AMR) codes. We find that the SPH simulations produce
larger temperature variations connected to the persistence of both
substructures and their stripped cold gas. This difference is more evident in
no-radiative simulations, while it is reduced in the presence of radiative
cooling. We also find that the temperature variation in radiative cluster
simulations is generally in agreement with the observed one in the central
regions of clusters. Around R_500 the temperature inhomogeneities of the SPH
simulations can generate twice the typical hydrostatic-equilibrium mass bias of
the AMR sample. We emphasize that a detailed understanding of the physical
processes responsible for the complex thermal structure in ICM requires
improved resolution and high sensitivity observations in order to extend the
analysis to higher temperature systems and larger cluster-centric radii.Comment: 13 pages, 12 figures, 4 table
Radio morphology and spectral analysis of cD galaxies in rich and poor galaxy clusters
We present a radio morphological study and spectral analysis for a sample of
13 cD galaxies in rich and poor clusters of galaxies.} Our study is based on
new high sensitivity Giant Metrewave Radio Telescope (GMRT) observations at
1.28 GHz, 610 MHz and 235 MHz, and on archival data. From a statistical sample
of cluster cD galaxies we selected those sources with little information
available in the literature and promising for the detection of aged radio
emission. Beyond the high sensitivity images for all 13 radio galaxies, we
present also a detailed spectral analysis for 7 of them. We found a variety of
morphologies and linear sizes, as typical for radio galaxies in the radio power
range sampled here (low to intermediate power radio galaxies). The spectral
analysis shows that 10/13 radio galaxies have steep radio spectrum, with
spectral index . In general, the radiative ages and growth
velocities are consistent with previous findings that the evolution of radio
galaxies at the cluster centres is affected by the dense external medium (i.e.
low growth velocities and old ages. We suggest that the dominant galaxies in A
2622 and MKW 03s are dying radio sources, which at present are not fed by
nuclear activity. On the other hand, the spectacular source at the centre of A
2372 might be a very interesting example of restarted radio galaxy. For this
source we estimated a life cycle of the order of 10 yr.Comment: Accepted by A&A, 25 pages, 28 figures, 6 tables and appendix Full
version including high quality images available at
http://www.ira.inaf.it/~tventuri/pap/Venturi.pd
An X-ray and optical study of the cluster A33
We report the first detailed X-ray and optical observations of the
medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the
UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray
and optical imaging and spectroscopic data allowed us to identify the X-ray
source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint,
F_{2-10 keV} \approx 2.4 \times 10^{-13} \ergscm2, X-ray source
1SAXJ0027.2-1930, arcmin away from the optical position of the cluster
as given in the Abell catalogue, is identified with the central region of A33.
Based on six cluster galaxy redshifts, we determine the redshift of A33,
; this is lower than the value derived by Leir and Van Den Bergh
(1977). The source X-ray luminosity, L_{2-10 keV} = 7.7 \times 10^{43} \ergs,
and intracluster gas temperature, keV, make this cluster interesting
for cosmological studies of the cluster relation at intermediate
redshifts. Two other X-ray sources in the A33 field are identified. An AGN at
z0.2274, and an M-type star, whose emission are blended to form an extended
X-ray emission arcmin north of the A33 cluster. A third possibly
point-like X-ray source detected arcmin north-west of A33 lies close
to a spiral galaxy at z0.2863 and to an elliptical galaxy at the same
redshift as the cluster.Comment: 9 pages, 6 Figures, Latex (using psfig,l-aa), to appear in Astronomy
and Astrophysics S. (To get better quality copies of Figs.1-3 send an email
to: [email protected]). A&AS, in pres
A radio minihalo in the extreme cool-core galaxy cluster RXCJ1504.1-0248
Aims. We report the discovery of a radio minihalo in RXCJ1504.1-0248, a
massive galaxy cluster that has an extremely luminous cool core. To date, only
9 radio minihalos are known, thus the discovery of a new one, in one of the
most luminous cool-core clusters, provides important information on this
peculiar class of sources and sheds light on their origin. Methods. The diffuse
radio source is detected using GMRT at 327 MHz and confirmed by pointed VLA
data at 1.46 GHz. The minihalo has a radius of 140 kpc. A Chandra gas
temperature map shows that the minihalo emission fills the cluster cool core
and has some morphological similarities to it, as has been previously observed
for other minihalos. Results. The Chandra data reveal two subtle cold fronts in
the cool core, likely created by sloshing of the core gas, as observed in most
cool-core clusters. Following previous work, we speculate that the origin of
the minihalo is related to sloshing. Sloshing may result in particle
acceleration by generating turbulence and/or amplifying the magnetic field in
the cool core, leading to the formation of a minihalo.Comment: 4 pages, 1 table, 3 color figures. Accepted for publication in A&A
Letter
Temperature and total mass profiles of the A3571 cluster of galaxies
We present BeppoSAX results of a spatially resolved spectral analysis of A3571, a relaxed nearby cluster of galaxies. In the central 2' (130/h_50 kpc) radius the metal abundance is 0.49 +- 0.08 solar and the absorption (1.13 +-0.28) x 10^21 atom/cm^2 whereas elsewhere within an 8'(520/h_50 kpc) radius the abundance is 0.32 \+- 0.05 solar and the absorption consistent with the galactic value of 4.4 x 10^20 atom/cm2. The significant central metal abundance enhancement is consistent with the supernova enrichment scenario. The excess absorption may be attributed to the cooling flow, whose mass flow rate is 80 +- 40 M_Sun/yr from our spectral fit. The BeppoSAX and ASCA radial temperature profiles agree over the entire overlapping radial range r < 25' = 1.6/h_50 Mpc. The combined BeppoSAX and ASCA temperature profile exhibits a constant value out to a radius of 10' (650/h_50 kpc) and a significant decrease (T propto r^-0.55, corresponding to gamma=1.28) at larger radii. These temperature data are used to derive the total mass profile. The best fit NFW dark matter density model results in a temperature profile that is not convectively stable, but the model is acceptable within the uncertainties of the data. The temperature profile is acceptably modeled with a ``core'' model for the dark matter density, consisting of a core radius with a constant slope at larger radii. With this model the total mass and formal 90% confidence errors within the virial radius r_178 (2.5/h_50 Mpc) are 9.1+3.6-1.5 x 10^14 h_50^-1 M_Sun, by a factor of 1.4 smaller than the isothermal value. The gas mass fraction increases with radius, reaching f_gas(r_178) = 0.26+0.05-0.10 x h_50^-3/2. Assuming that the measured gas mass fraction is the lower limit to the primordial baryonic fraction gives Omega_m < 0.4 at 90% confidence
Tracing baryons in the warm-hot intergalactic medium with broad Ly alpha absorption
We discuss physical properties and baryonic content of broad Ly alpha
absorbers (BLAs) at low redshift. These absorption systems, recently discovered
in high-resolution, high-signal to noise quasar absorption line spectra,
possibly trace the warm-hot intergalactic medium (WHIM) in the temperature
range between 10^5 and 10^6 K. To extend previous BLA measurements we have
analyzed STIS data of the two quasars H 1821+643 and PG 0953+415 and have
identified 13 BLA candidates along a total (unblocked) redshift path of
dz=0.440. Combining our measurements with previous results for the lines of
sight toward PG 1259+593 and PG 1116+215, the resulting new BLA sample consists
of 20 reliably detected systems as well as 29 additional tentative cases,
implying a BLA number density of dN/dz=22-53. We estimate that the contribution
of BLAs to the baryon density at z=0 is Omega_b(BLA)>0.0027 h_70^-1 for
absorbers with log (N/b)>11.3. This number indicates that WHIM broad Ly alpha
absorbers contain a substantial fraction of the baryons in the local Universe.
(Abridged abstract)Comment: 17 pages, 7 figures; Accepted for publication in A&
Searching for AGN-driven Shocks in Galaxy Clusters
Shocks and blastwaves are expected to be driven driven into the intracluster
medium filling galaxy groups and clusters by powerful outbursts of active
galactic nuclei or quasars in the member galaxies; the first footprints of
shock fronts have been tentatively traced out with X-ray imaging. We show how
overpressures in the blasts behind the shock can prove the case and also
provide specific marks of the nuclear activity: its strength, its current
stage, and the nature of its prevailing output. We propose to detect these
marks with the aimed pressure probe constituted by the resolved
Sunyaev-Zel'dovich effect. We compute and discuss the outcomes to be expected
in nearby and distant sources at different stages of their activity.Comment: 4 pages, 1 figure, uses REVTeX4 + emulateapj.cls and apjfonts.sty.
Accepted on ApJ
Complete Healing of a Giant Wart in a Severely Immune-Compromised Patient with HIV Infection Treated with Acupuncture
Giant warts are infrequent dermatological viral infections caused by Papillomavirus (HPV) in immune-compromised patients. Treatment may often be difficult and unsatisfactory, either by surgery or cytotoxic agents, because of poor immune control of viral activity in such hosts. Here we report on the case of a patient with advanced and persistent immune suppression caused by HIV disease, who developed a monstrous wart covering the entirety of the radial district of his right hand. He was completely healed after a long treatment with traditional Chinese acupuncture, in spite of minimal immune recovery induced by efficacious antiretroviral therapy. To the best of our knowledge, therefore, the present report may be the first direct clinical evidence that acupuncture may be effective in the treatment of cutaneous warts also in HIV-infected patients
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