Relativistic Electrons & Magnetic Fields in Clusters of Galaxies

RXTE and BeppoSAX observations have yielded evidence for the presence of a secondary power-law spectral component in the spectra of several clusters of galaxies. This emission in clusters with extended regions of radio emission is likely to be by relativistic electrons that are Compton scattered by the CMB. The radio and non-thermal (NT) X-ray measurements yield the values of the volume-averaged magnetic field and electron energy density in the cluster extragalactic environment. These directly deduced quantities provide a tangible basis for the study of NT phenomena in clusters.Comment: 3 pages, 1 figure, to be published in proceedings of the 10th Marcel Grossmann meetin

The Sunyaev-Zeldovich Effect: Current Status and Future Prospects

The detailed spectral and spatial characteristics of the signature imprinted on the cosmic microwave background (CMB) radiation by Compton scattering of the radiation by electrons in the hot gas in clusters of galaxies - the Sunyaev-Zeldovich (S-Z) effect - are of great astrophysical and cosmological significance. In recent years observations of the effect have improved tremendously; high signal-to-noise images of the effect (at low microwave frequencies) can now be obtained by interferometric arrays. In the near future, high frequency measurements of the effect will be made with ground based and balloon-borne telescopes equipped with bolometeric arrays. Towards the end of the decade the PLANCK satellite will carry out an extensive S-Z survey over a wide frequency range. Along with the improved observational capabilities, the theoretical description of the effect, and its use as a precise cosmological probe, have been considerably advanced. In this review, I briefly discuss the nature and significance of the effect, its exact theoretical description, the current observational status, and prospects for the near future.Comment: Invited review, proceedings of the 9th Marcel Grossmann Meeting; 10 pages, 4 figure

Is there a hard tail in the Coma Cluster X-ray spectrum?

We report results from a re-analysis of the BeppoSAX observation of Coma and from the analysis of a second, yet unpublished observation of the same object. From our re-analysis of the first observation we find that the statistical evidence for a hard tail is about 2 sigma. From the analysis of the second observation which, thanks to the lower background and the longer exposure time, is characterized by a larger signal to noise we find no evidence for a hard tail. From the upper limit on the flux of the hard tail, using the standard Inverse Compton formulae, we derive a lower limit for the magnetic of about 0.2-0.4 microGauss consistent with Faraday rotation measurements.Comment: 4 pages, 2 figures, to appear in A&A Letter

Sunyaev-Zeldovich Cluster Counts as a Probe of Intra-Supercluster Gas

X-ray background surveys indicate the likely presence of diffuse warm gas in the Local Super Cluster (LSC), in accord with expectations from hydrodynamical simulations. We assess several other manifestations of warm LSC gas; these include anisotropy in the spatial pattern of cluster Sunyaev-Zeldovich (S-Z) counts, its impact on the CMB temperature power spectrum at the lowest multipoles, and implications on measurements of the S-Z effect in and around the Virgo cluster.Comment: 14 pages, 6 figures, draft versio

High Energy Phenomena in Clusters of Galaxies

Several phenomena in high energy astrophysics have been recently related to clusters of galaxies and to cosmic ray interactions occurring inside these structures. In many of these phenomena the observable effects depend on the energy density of cosmic rays confined in the Intra Cluster (IC) medium, which is a poorly known quantity. We propose here that useful indications about this quantity can be obtained from present and future observations of galaxy clusters in the radio and hard X-ray frequency ranges.Comment: 5 pages, 3 Figures, Latex (using espcrc2,epsfig), to appear in the Proceedings of the TAUP97, Eds. A. DiCredico et al., in press. Send comments to S.Colafrancesco: [email protected]

Neutrino Mass from SZ Surveys

The expected sensitivity of cluster SZ number counts to neutrino mass in the sub-eV range is assessed. We find that from the ongoing {\it Planck}/SZ measurements the (total) neutrino mass can be determined at a (1-sigma) precision of 0.06 eV, if the mass is in the range 0.1-0.3 eV, and the survey detection limit is set at the 5-sigma significance level. The mass uncertainty is predicted to be lower by a factor ~2/3, if a similar survey is conducted by a cosmic-variance-limited experiment, a level comparable to that projected if CMB lensing extraction is accomplished with the same experiment. At present, the main uncertainty in modeling cluster statistical measures reflects the difficulty in determining the mass function at the high-mass end.Comment: 8 pages, Proceedings of the 13th Marcel Grossmann Meetin

High-energy emission from star-forming galaxies

Adopting the convection-diffusion model for energetic electron and proton propagation, and accounting for all the relevant hadronic and leptonic processes, the steady-state energy distributions of these particles in the starburst galaxies M82 and NGC253 can be determined with a detailed numerical treatment. The electron distribution is directly normalized by the measured synchrotron radio emission from the central starburst region; a commonly expected theoretical relation is then used to normalize the proton spectrum in this region, and a radial profile is assumed for the magnetic field. The resulting radiative yields of electrons and protons are calculated: the predicted >100MeV and >100GeV fluxes are in agreement with the corresponding quantities measured with the orbiting Fermi telescope and the ground-based VERITAS and HESS Cherenkov telescopes. The cosmic-ray energy densities in central regions of starburst galaxies, as inferred from the radio and gamma-ray measurements of (respectively) non-thermal synchrotron and neutral-pion-decay emission, are U=O(100) eV/cm3, i.e. at least an order of magnitude larger than near the Galactic center and in other non-very-actively star-forming galaxies. These very different energy density levels reflect a similar disparity in the respective supernova rates in the two environments. A L(gamma) ~ SFR^(1.4) relationship is then predicted, in agreement with preliminary observational evidence.Comment: Invited talk at SciNeGHE2010 (8th Wotkshop on Science with the New Generation of High Energy Gamma-ray Experiments): Gamma-ray Astrophysics in the Multimessenger Context (Trieste, Sept.8-10, 2010