255 research outputs found

    Cosmic-Ray Proton to Electron Ratios

    Full text link
    A basic quantity in the characterization of relativistic particles is the proton-to-electron (p/e) energy density ratio. We derive a simple approximate expression suitable to estimate this quantity, U_p/U_e = (m_p/m_e)^(3-q)/2, valid when a nonthermal `gas' of these particles is electrically neutral and the particles' power-law spectral indices are equal -- e.g., at injection. This relation partners the well-known p/e number density ratio at 1 GeV, i.e. N_p/N_e = (m_p/m_e)^{(q-1)/2}.Comment: 4 pages; to be published in Proc. of MGM13 (13th Marcel Grossmann Meeting -- Stockholm July 1-7, 2012

    Impact of a non-Gaussian density field on Sunyaev-Zeldovich observables

    Full text link
    The main statistical properties of the Sunyaev-Zeldovich (S-Z) effect - the power spectrum, cluster number counts, and angular correlation function - are calculated and compared within the framework of two density fields which differ in their predictions of the cluster mass function at high redshifts. We do so for the usual Press and Schechter mass function, which is derived on the basis of a Gaussian density fluctuation field, and for a mass function based on a chi^2 distributed density field. These three S-Z observables are found to be very significantly dependent on the choice of the mass function. The different predictions of the Gaussian and non-Gaussian density fields are probed in detail by investigating the behaviour of the three S-Z observables in terms of cluster mass and redshift. The formation time distribution of clusters is also demonstrated to be sensitive to the underlying mass function. A semi-quantitative assessment is given of its impact on the concentration parameter and the temperature of intracluster gas.Comment: 17 pages, 11 figures, accepted for publication in MNRA

    The Effects of Relativistic Corrections on Cosmological Parameter Estimations from SZE Cluster Surveys

    Full text link
    Sunyaev-Zel'dovich Effect (SZE) cluster surveys are anticipated to yield tight constraints on cosmological parameters such as the equation of state of dark energy. In this paper, we study the impact of relativistic corrections of the thermal SZE on the cluster number counts expected from a cosmological model and thus, assuming that other cosmological parameters are known to high accuracies, on the determination of the ww parameter and σ8\sigma_8 from a SZE cluster survey, where w=p/ρw=p/\rho with pp the pressure and ρ\rho the density of dark energy, and σ8\sigma_8 is the rms of the extrapolated linear density fluctuation smoothed over 8Mpch18\hbox{Mpc}h^{-1}. For the purpose of illustrating the effects of relativistic corrections, our analyses mainly focus on ν=353GHz\nu=353 \hbox{GHz} and Slim=30mJyS_{lim}=30\hbox{mJy}, where ν\nu and SlimS_{lim} are the observing frequency and the flux limit of a survey, respectively. These observing parameters are relevant to the {\it Planck} survey. It is found that from two measurable quantities, the total number of SZE clusters and the number of clusters with redshift z0.5z\ge 0.5, σ8\sigma_8 and ww can be determined to a level of ±1\pm 1% and ±8\pm 8%, respectively, with 1σ1\sigma uncertainties from a survey of 10000deg210000\hbox{deg}^2. Relativistic effects are important in determining the central values of σ8\sigma_8 and ww. If we choose the two quantities calculated relativistically from the flat cosmological model with σ8=0.8284\sigma_8=0.8284 and w=0.75w=-0.75 as input, the derived σ8\sigma_8 and ww would be 0.819 and -0.81, respectively, if relativistic effects are wrongly neglected. The location of the resulting σ8\sigma_8 and ww in the σ8w\sigma_8-w plane is outside the 3σ3\sigma region around the real central σ8\sigma_8 and ww.Comment: ApJ in pres

    On the origin of extinction in the Coma cluster of galaxies

    Get PDF
    Visual extinction of distant clusters seen through the Coma cluster seem to suggest that dust may be present in the hot x ray emitting intracluster gas. However, the Infrared Astronomy Satellite (IRAS) failed to detect any infrared emission from the cluster at the level expected from the extinction measurements. Researchers carried out a detailed analysis of the properties of intracluster dust in the context of a model which includes continuous injection of dust by the cluster galaxies, grain destruction by sputtering, and transient grain heating by the hot plasma. Computed infrared fluxes are in agreement with the upper limit obtained from the IRAS. The calculations, and the constraint implied by the IRAS observations, suggest that the intracluster dust must be significantly depleted compared to interstellar abundances. Researchers discuss possible explanations for the discrepancy between the observed visual extinction and the IRAS upper limit

    The Sunyaev-Zeldovich Effect and Its Cosmological Significance

    Get PDF
    Comptonization of the cosmic microwave background (CMB) radiation by hot gas in clusters of galaxies - the Sunyaev-Zeldovich (S-Z) effect - is 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 ground-based interferometric arrays. In the near future, high frequency measurements of the effect will be made with bolomateric arrays during long duration balloon flights. Towards the end of the decade the PLANCK satellite will extensive S-Z surveys over a wide frequency range. Along with the improved observational capabilities, the theoretical description of the effect and its more precise use as a probe have been considerably advanced. I review the current status of theoretical and observational work on the effect, and the main results from its use as a cosmological probe.Comment: Invited review; in proceedings of the Erice NATO/ASI `Astrophysical Sources of High Energy Particles and Radiation'; 11 pages, 3 figure

    Determination of cosmological parameters: an introduction for non-specialists

    Get PDF
    I start by defining the cosmological parameters H0,ΩmH_0, \Omega_m and ΩΛ\Omega_\Lambda. Then I show how the age of the universe depends on them, followed by the evolution of the scale parameter of the universe for various values of the density parameters. Then I define strategies for measuring them, and show the results for the recent determination of these parameters from measurements on supernovas of type 1a. Implications for particle physics is briefly discussed at the end.Comment: 12 pages, Latex with epsf.sty. Invited talk at the ``Discussion meeting on Recent Developments in Neutrino Physics'', held at the Physical Research Laboratory, Ahmedabad, February 2--4, 199
    corecore