531 research outputs found
Warming rays in cluster cool cores
We present a model of cosmic ray heating of clusters' cores that reproduces
the observed temperature distribution in clusters by using an energy balance
condition in which the emitted X-ray energy is supplied by the hadronic cosmic
rays, which act as warming rays (WRs). The temperature profile of the IC gas is
correlated with the WR pressure distribution and, consequently, with the
non-thermal emission (radio, hard X-ray and gamma-ray) induced by the
interaction of the WRs with the IC gas and magnetic field. The temperature
distribution of the IC gas in both cool-core and non cool-core clusters is
successfully predicted from the measured IC gas density distribution. Under
this contraint, the WR model is also able to reproduce the thermal and
non-thermal pressure distribution in clusters, as well as their radial entropy
distribution. The WR model provides other observable features: a correlation of
the pressure ratio (WRs to thermal IC gas) with the inner cluster temperature
T_{inner}, a correlation of the gamma-ray luminosity with T_{inner}, a
substantial number of cool-core clusters observable with the GLAST-LAT
experiment, a surface brightness of radio halos in cool-core clusters that
recovers the observed one, a hard X-ray emission from cool-core clusters that
is systematically lower than the observed limits and yet observable with the
next generation HXR experiments like Simbol-X. The specific theoretical
properties and the multi-frequency distribution of the e.m. signals predicted
in the WR model render it quite different from the other models proposed for
the heating of clusters' cool-cores. Such differences make it possible to prove
or disprove our model as an explanation of the cooling-flow problems on the
basis of multi-frequency observations of galaxy clusters.Comment: 19 pages, 17 figures, A&A in pres
Spatial features of non-thermal SZ effect in galaxy clusters
We investigate the spatial behaviour of the total comptonization parameter
evaluated for a galaxy cluster containing two population of
electrons: the thermal population, with energy around some KeV and whose trace
is evident in the X-ray emission of the ICM (Intra-Cluster Medium), and the
relativistic population, which give rise to the radio halo emission found in
several clusters of galaxies. We present the first results obtained from our
analysis showing that there are remarkable features in such spatial trend,
which might throw a new light in understanding the cluster internal processes.Comment: 4 pages, 1 figure, to appear in the proceedings of the 2k1bc workshop
""Experimental comsology @ millimetre wavelengths", july 9-12 2001,
Breuil-Cervinia, Ital
A multi-frequency study of the SZE in giant radio galaxies
Radio-galaxy (RG) lobes contain relativistic electrons embedded in a tangled
magnetic field that produce, in addition to low-frequency synchrotron radio
emission, inverse-Compton scattering (ICS) of the cosmic microwave background
(CMB) photons. This produces a relativistic, non-thermal Sunyaev-Zel'dovich
effect (SZE). We study the spectral and spatial properties of the non-thermal
SZE in a sample of radio galaxies and make predictions for their detectability
in both the negative and the positive part of the SZE, with space experiments
like Planck, OLIMPO, and Herschel-SPIRE. These cover a wide range of
frequencies, from radio to sub-mm. We model the SZE in a general formalism that
is equivalent to the relativistic covariant one and describe the electron
population contained in the lobes of the radio galaxies with parameters derived
from their radio observations, namely, flux, spectral index, and spatial
extension. We further constrain the electron spectrum and the magnetic field of
the RG lobes using X-ray, gamma-ray, and microwave archival observations. We
determine the main spectral features of the SZE in RG lobes, namely, the
minimum, the crossover, and the maximum of the SZE. We show that these typical
spectral features fall in the frequency ranges probed by the available space
experiments. We provide the most reliable predictions for the amplitude and
spectral shape of the SZE in a sample of selected RGs with extended lobes. In
three of these objects, we also derive an estimate of the magnetic field in the
lobe at the muG level by combining radio (synchrotron) observations and X-ray
(ICS) observations. These data, together with the WMAP upper limits, set
constraints on the minimum momentum of the electrons residing in the RG lobes
and allow realistic predictions for the visibility of their SZE to be derived
with Planck, OLIMPO, and Herschel-SPIRE. [abridged]Comment: 26 pages, 21 figures; Astronomy and Astrophysics, in pres
Polarization of the Sunyaev-Zel'dovich effect: relativistic imprint of thermal and non-thermal plasma
[Abridged] Inverse Compton scattering of CMB fluctuations off cosmic electron
plasma generates a polarization of the associated Sunyaev-Zel'dovich (SZ)
effect. This signal has been studied so far mostly in the non-relativistic
regime and for a thermal electron population and, as such, has limited
astrophysical applications. Partial attempts to extend this calculation for a
thermal electron plasma in the relativistic regime have been done but cannot be
applied to a general relativistic electron distribution. Here we derive a
general form of the SZ effect polarization valid in the full relativistic
approach for both thermal and non-thermal electron plasmas, as well as for a
generic combination of various electron population co-spatially distributed in
the environments of galaxy clusters or radiogalaxy lobes. We derive the
spectral shape of the Stokes parameters induced by the IC scattering of every
CMB multipole, focusing on the CMB quadrupole and octupole that provide the
largest detectable signals in galaxy clusters. We found that the CMB quadrupole
induced Stoke parameter Q is always positive with a maximum amplitude at 216
GHz which increases slightly with increasing cluster temperature. The CMB
octupole induced Q spectrum shows, instead, a cross-over frequency which
depends on the cluster electron temperature, or on the minimum momentum p_1 as
well as on the power-law spectral index of a non-thermal electron population.
We discuss some possibilities to disentangle the quadrupole-induced Q spectrum
from the octupole-induced one which allow to measure these quantities through
the SZ effect polarization. We finally apply our model to the realistic case of
the Bullet cluster and derive the visibility windows of the total,
quandrupole-induced and octupole-induced Stoke parameter Q in the frequency
ranges accessible to SKA, ALMA, MILLIMETRON and CORE++ experiments.Comment: 31 pages, 11 figures, submitted to JCA
Multi-frequency constraints on the non-thermal pressure in galaxy clusters
The origin of radio halos in galaxy clusters is still unknown and is the
subject of a vibrant debate both from the observational and theoretical point
of view. In particular the amount and the nature of non-thermal plasma and of
the magnetic field energy density in clusters hosting radio halos is still
unclear. The aim of this paper is to derive an estimate of the pressure ratio X
between the non-thermal and thermal plasma in radio halo clusters that have
combined radio, X-ray and SZ effect observations. From the simultaneous
P_{1.4}-L_X and P_{1.4}-Y_{SZ} correlations for a sample of clusters observed
with Planck, we derive a correlation between Y_{SZ} and L_X that we use to
derive a value for X. This is possible since the Compton parameter Y_{SZ} is
proportional to the total plasma pressure in the cluster (that we characterize
as the sum of the thermal and non-thermal pressure) while the X-ray luminosity
L_X is proportional only to the thermal pressure of the intracluster plasma.
Our results indicate that the average (best fit) value of the pressure ratio in
a self-similar cluster formation model is X =0.55 \pm 0.05 in the case of an
isothermal beta-model with beta=2/3 and a core radius r_c = 0.3 R_{500} holding
on average for the cluster sample. We also show that the theoretical prediction
for the Y_{SZ}-L_X correlation in this model has a slope that is steeper than
the best fit value for the available data. The agreement with the data can be
recovered if the pressure ratio X decreases with increasing X-ray luminosity as
L_X^{-0.96}. We conclude that the available data on radio halo clusters
indicate a substantial amount of non-thermal pressure in cluster atmospheres
whose value must decrease with increasing X-ray luminosity, or increasing
cluster mass (temperature). (abridged)Comment: A&A, in press; 10 pages; 10 figure
Effect of the non-thermal Sunyaev–Zel’dovich effect on the temperature determination of galaxy clusters
A recent stacking analysis of Planck HFI data of galaxy clusters led to the derivation of the cluster temperatures using the relativistic corrections to the Sunyaev-Zel'dovich effect (SZE). However, the temperatures of high-temperature clusters, as derived from this analysis, were basically higher than the temperatures derived from X-ray measurements, at a moderate statistical significance of 1.5 sigma. This discrepancy has been attributed by Hurier to calibration issues. In this paper, we discuss an alternative explanation for this discrepancy in terms of a non-thermal SZE astrophysical component. We find that this explanation can work if non-thermal electrons in galaxy clusters have a low minimum momentum (p(1) similar to 0.5-1), and if their pressure is of the order of 20-30 per cent of the thermal gas pressure. Both these conditions are hard to obtain if the non-thermal electrons are mixed with the hot gas in the intracluster medium, but can be possibly obtained if the non-thermal electrons are mainly confined in bubbles with a high amount of non-thermal plasma and a low amount of thermal plasma, or are in giant radio lobes/relics in the outskirts of the clusters. To derive more precise results on the properties of the non-thermal electrons in clusters, and in view of more solid detections of a discrepancy between X-ray- and SZE-derived cluster temperatures that cannot be explained in other ways, it would be necessary to reproduce the full analysis done by Hurier by systematically adding the non-thermal component of the SZE.EM201
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