816 research outputs found
Dark Matter in Modern Cosmology
The presence of Dark Matter (DM) is required in the universe regulated by the
standard general relativistic theory of gravitation. The nature of DM is
however still elusive to any experimental search. We discuss here the process
of accumulation of evidence for the presence of DM in the universe, the
astrophysical probes for the leading DM scenarios that can be obtained through
a multi-frequency analysis of cosmic structures on large scales, and the
strategies related to the multi-messenger and multi-experiment astrophysical
search for the nature of the DM.Comment: 25 pages, 9 figures. Updated version of the review included in
ASTROPHYSICS AND COSMOLOGY AFTER GAMOW: Proceedings of the 4th Gamow
International Conference on Astrophysics and Cosmology After Gamow and the
9th Gamow Summer School "Astronomy and Beyond: Astrophysics, Cosmology, Radio
Astronomy, High Energy Physics and Astrobiology". AIP Conference Proceedings,
Volume 1206, p.
On the ability of spectroscopic SZ effect measurements to determine the temperature structure of galaxy clusters
(abridged) We explore in this paper the ability of spatially resolved
spectroscopic measurements of the SZ effect (SZE) to determine the temperature
profile of galaxy clusters. We derive a general formalism for the thermal SZE
in galaxy clusters with a non-uniform temperature profile that can be applied
to both cool-core clusters and non-cool core cluster with an isothermal or
non-isothermal temperature structure. We derive an inversion technique through
which the electron distribution function can be extracted from spectroscopic
SZE observations over a wide frequency range. We study the fitting procedure to
extract the cluster temperature from a set of simulated spatially resolved
spectroscopic SZE observations in different bands of the spectrum, from 100 to
450 GHz. The results of our analysis for three different cluster prototypes
(A2199 with a low-temperature cool core, Perseus with a relatively
high-temperature cool core, Ophiuchus with an isothermal temperature
distribution) provide both the required precision of the SZE observations and
the optimal frequency bands for a determination of the cluster temperature
similar or better than that obtainable from X-ray observations. The precision
of SZE-derived temperature is also discussed for the outer regions of clusters.
We also study the possibility to extract, from our method, the parameters
characterizing the non-thermal SZE spectrum of the relativistic plasma
contained in the lobes of radio galaxies as well as the spectrum of
relativistic electrons co-spatially distributed with the thermal plasma in
clusters with non-thermal phenomena. We find that the next generation SZE
experiments with spectroscopic capabilities can provide precise temperature
distribution measurements (...)Comment: Submitted to Astronomy & Astrophysic
Evidence for a Significant Blazar Contamination in CMB Anisotropy Maps
The analysis of the recent WMAP source catalog shows that the vast majority
of bright foreground extragalactic sources detected in CMB maps are Blazars. In
this paper we calculate the contamination of CMB anisotropy maps by this type
of flat-spectrum, strongly variable and polarized extragalactic radio sources
using up-to-date results from recent deep multi-frequency surveys. We found
that more than 50 known Blazars (or Blazar candidates) are included in the
90/150 GHz BOOMERANG anisotropy maps, a factor > 15 larger than previously
reported. Using a recent derivation of the Blazar radio LogN-LogS we calculate
that these sources induce an average sky brightness of 0.2 Jy/deg^2,
corresponding to an average temperature of ~3-5 muK. Moreover, we find that the
associated level of fluctuations is of the order of C_{l, Blazar}= 1.3 10^{-2}
mu K^2 sr at 41 GHz. Taking into account both Blazar variability and the many
steep-spectrum radio sources that flatten at high frequencies, as well as the
contribution of radio-galaxies, we find that the level of residual fluctuation
due to discrete extragalactic foreground sources could be factor of ~2 - 3
higher than the above estimate. We show that the Blazar induced fluctuations
contaminate the CMB spectrum at the level of ~ 20-50 % at l = 500 and 50-100 %
at l = 800. Careful cleaning for Blazar contamination of high sensitivity/high
resolution CMB maps is therefore necessary before firm conclusions about weak
features, like secondary high-l peaks of the CMB power spectrum or very weak
signals like CMB polarization measurements, can be achieved.Comment: 10 pages, 6 Postscript figures, 1 GIF figure (Fig.3). Better version
of Fig.3 and a full list of Blazar's SED found at
http://www.asdc.asi.it/boomerang/. A&A, submitte
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
Cosmic Rays, Radio Halos and Non-Thermal X-ray Emission in Clusters of Galaxies
We calculate the flux of radio, hard X-ray and UV radiation from clusters of
galaxies as produced by synchrotron emission and Inverse Compton Scattering of
electrons generated as secondaries in cosmic ray interactions in the
intracluster medium. Both the spatial distribution of cosmic rays due to their
diffusion and the spatial distribution of the intracluster gas are taken into
account. Our calculations are specifically applied to the case of the Coma
cluster. The fluxes and spectra of the radio halo emission and of the hard
X-ray excess from Coma can be explained in this model if an average magnetic
field is assumed. However, such a low value for the
intracluster magnetic field implies a large cosmic ray energy density which in
turn is responsible, through neutral pion decay, for a gamma ray flux above 100
MeV which exceeds the EGRET upper limit. This gamma ray bound can be relaxed if
the hard X-ray excess and the radio halo emission from Coma are not due to the
same population of electrons. We finally stress the unique role that the new
generation gamma ray satellites will play to discriminate among different
models for the non thermal emission in clusters of galaxies.Comment: 25 pages, 3 Figures, Latex (using epsfig,elsart), to appear in
Astroparticle Physics. Astroparticle Physics, in pres
On the ICS interpretation of the Hard X-Ray Excesses in Galaxy Clusters: the case of Ophiuchus
(Abridged) High-E electrons produce Hard X-Ray (HXR) emission in galaxy
clusters by via Inverse Compton Scattering (ICS) of CMB photons. We derive the
ICS HXR emission of Ophiuchus under various scenarios: primary cosmic ray
model, secondary cosmic rays model and neutralino DM annihilation scenario. We
further discuss the predictions of the Warming Ray model for the cluster
atmosphere. Under the assumption to fit the observed HXR emission, we find that
the high-E electrons induce various consequences on the cluster atmosphere: i)
primary electrons can be marginally consistent with the data provided that
their spectrum is cutoff at E~30(90) MeV for spectral index of 3.5 (4.4); ii)
secondary electron models from pp collisions are inconsistent with gamma-ray
limits, cosmic ray protons produce too much heating of the IC gas and their
pressure at the cluster center largely exceeds the thermal one; iii) secondary
electron models from DM annihilation are inconsistent with gamma-ray and radio
limits and electrons produce too much heating of the IC gas at the cluster
center, unless the neutralino annihilation cross section is much lower than the
proposed value. We conclude that ICS by secondary electrons from both
neutralino DM annihilation and pp collisions cannot be the mechanism
responsible for the HXR excess emission; primary electrons are still a
marginally viable solution provided that their spectrum has a low-energy cutoff
at E~30-90 MeV. The WR model offers, so far, the best description of the
cluster in terms of temperature distribution, heating, pressure and spectral
energy distribution. Fermi observations of Ophiuchus will set further
constraints to this model.Comment: 10 pages, 9 figures, A&A in pres
A possible theoretical explanation of metallicity gradients in elliptical galaxies
Models of chemical evolution of elliptical galaxies taking into account
different escape velocities at different galactocentric radii are presented. As
a consequence of this, the chemical evolution develops differently in different
galactic regions; in particular, we find that the galactic wind, powered by
supernovae (of type II and I) starts, under suitable conditions, in the outer
regions and successively develops in the central ones. The rate of star
formation (SFR) is assumed to stop after the onset of the galactic wind in each
region. The main result found in the present work is that this mechanism is
able to reproduce metallicity gradients, namely the gradients in the
index, in good agreement with observational data. We also find that in order to
honor the constant [Mg/Fe] ratio with galactocentric distance, as inferred from
metallicity indices, a variable initial mass function as a function of
galactocentric distance is required. This is only a suggestion since trends on
abundances inferred just from metallicity indices are still uncertain.Comment: 18 pages, LaTeX file with 4 figures using mn.sty, submitted to MNRA
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