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

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 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 $Mg_2$ 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

Spatial features of non-thermal SZ effect in galaxy clusters

We investigate the spatial behaviour of the total comptonization parameter $y_{tot}$ 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

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

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

Evolution of Dark Matter Halos and their Radio Emissions

Radio synchrotron emission is expected as a natural by-product of the self-annihilation of super-symmetric dark matter particles. In this work we discuss the general properties of the radio emission expected in a wide range of dark matter halos, from local dwarf spheroidal galaxies to large and distant galaxy clusters with the aim to determine the neutralino dark matter detection prospects of the Square Kilometre Array (SKA). The analysis of the SKA detection of dark matter(DM)-induced radio emission is presented for structures spanning a wide range of masses and redshifts, and we also analyze the limits that the SKA can set on the thermally averaged neutralino annihilation cross-section in the event of non-detection. To this aim, we construct a model of the redshift evolution of the radio emissions of dark matter halos and apply it to generate predicted fluxes from a range of neutralino masses and annihilation channels for the dark matter halos surrounding dwarf galaxies, galaxies and galaxy clusters. Using the available SKA performance predictions and its ability to determine an independent measure of the magnetic field in cosmic structures, we explore both the detailed detection prospects and the upper-bounds that might be placed on the neutralino annihilation cross-section in the event of non-detection. We find that the SKA can access a neutralino parameter space far larger than that of any preceding indirect-detection experiment, also improving on the realistic CTA detection prospects, with the possibility of setting cross-section upper-bounds up to four orders of magnitude below the thermal relic density bound. Additionally, we find that neutralino radio emissions carry redshift-independent signatures of the dominant annihilation channel and of neutralino mass, offering therefore a means to identify such non-thermal emissions within the observing frequency range of the SKA.Comment: 30 pages, 37 figures, submitted to JCA