221 research outputs found

    The Sunyaev-Zel'dovich angular power spectrum as a probe of cosmological parameters

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    The angular power spectrum of the SZ effect, C_l, is a powerful probe of cosmology. It is easier to detect than individual clusters in the field, is insensitive to observational selection effects and does not require a calibration between cluster mass and flux, reducing the systematic errors which dominate the cluster-counting constraints. It receives a dominant contribution from cluster region between 20-40% of the virial radius and is thus insensitive to the poorly known gas physics in the cluster centre, such as cooling or (pre)heating. In this paper we derive a refined analytic prediction for C_l using the universal gas-density and temperature profile and the dark-matter halo mass function. The predicted C_l has no free parameters and fits all of the published hydrodynamic simulation results to better than a factor of two around l=3000. We find that C_l scales as (sigma_8)^7 times (Omega_b h)^2 and is almost independent of all of the other cosmological parameters. This differs from the local cluster abundance studies, which give a relation between sigma_8 and Omega_m. We also compute the covariance matrix of C_l using the halo model and find a good agreement relative to the simulations. We estimate how well we can determine sigma_8 with sampling-variance-limited observations and find that for a several-square-degree survey with 1-2 arcminute resolution one should be able to determine sigma_8 to within a few percent, with the remaining uncertainty dominated by theoretical modelling. If the recent excess of the CMB power on small scales reported by the CBI experiment is due to the SZ effect, then we find sigma_8(Omega_b h/0.029)^0.3 = 1.04 +- 0.12 at the 95% confidence level (statistical) and with a residual 10% systematic (theoretical) uncertainty.Comment: 17 pages, 14 figures, 1 table, sigma8 constraint including CBI and BIMA, matches the accepted version in MNRA

    Constraints on the annihilation cross section of dark matter particles from anisotropies in the diffuse gamma-ray background measured with Fermi-LAT

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    Annihilation of dark matter particles in cosmological halos (including a halo of the Milky Way) contributes to the diffuse gamma-ray background (DGRB). As this contribution will appear anisotropic in the sky, one can use the angular power spectrum of anisotropies in DGRB to constrain properties of dark matter particles. By comparing the updated analytic model of the angular power spectrum of DGRB from dark matter annihilation with the power spectrum recently measured from the 22-month data of Fermi Large Area Telescope (LAT), we place upper limits on the annihilation cross section of dark matter particles as a function of dark matter masses. We find that the current data exclude <\sigma v> >~ 10^{-25} cm^3 s^{-1} for annihilation into b\bar{b} at the dark matter mass of 10 GeV, which is a factor of three times larger than the canonical cross section. The limits are weaker for larger dark matter masses. The limits can be improved further with more Fermi-LAT data as well as by using the power spectrum at lower multipoles (l <~ 150), which are currently not used due to a potential Galactic foreground contamination.Comment: 13 pages, 18 figures, comments welcom

    AKARI near-infrared background fluctuations arise from normal galaxy populations

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    We show that measurements of the fluctuations in the near-infrared background (NIRB) from the AKARI satellite can be explained by faint galaxy populations at low redshifts. We demonstrate this using reconstructed images from deep galaxy catalogs (HUGS/S-CANDELS) and two independent galaxy population models. In all cases, we find that the NIRB fluctuations measured by AKARI are consistent with faint galaxies and there is no need for a contribution from unknown populations. We find no evidence for a steep Rayleigh-Jeans spectrum for the underlying sources as previously reported. The apparent Rayleigh-Jeans spectrum at large angular scales is likely a consequence of galaxies being removed systematically to deeper levels in the longer wavelength channels.Comment: Submitted to MNRAS Letter

    Limits on anisotropic inflation from the Planck data

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    Temperature anisotropy of the cosmic microwave background offers a test of the fundamental symmetry of spacetime during cosmic inflation. Violation of rotational symmetry yields a distinct signature in the power spectrum of primordial fluctuations as P(k)=P0(k)[1+g(k^E^cl)2]P({\mathbf k})=P_0(k)[1+g_*(\hat{\mathbf k}\cdot\hat{\mathbf E}_{\rm cl})^2], where E^cl\hat{\mathbf E}_{\rm cl} is a preferred direction in space and gg_* is an amplitude. Using the \textit{Planck} 2013 temperature maps, we find no evidence for violation of rotational symmetry, g=0.002±0.016g_*=0.002\pm 0.016 (68% CL), once the known effects of asymmetry of the \textit{Planck} beams and Galactic foreground emission are removed.Comment: 5 pages, 2 figures. (v2) References added. A typo fixed. (v3) Various confidence levels included, Journal reference added (v4) error of a duplicated pdf file fixe

    Constraints on primordial magnetic fields from the optical depth of the cosmic microwave background

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    Damping of magnetic fields via ambipolar diffusion and decay of magnetohydrodynamical (MHD) turbulence in the post decoupling era heats the intergalactic medium (IGM). Delayed recombination of hydrogen atoms in the IGM yields an optical depth to scattering of the cosmic microwave background (CMB). The optical depth generated at z10z\gg 10 does not affect the "reionization bump" of the CMB polarization power spectrum at low multipoles, but affects the temperature and polarization power spectra at high multipoles. Writing the present-day energy density of fields smoothed over the damping scale at the decoupling epoch as ρB,0=B02/2\rho_{B,0}=B_{0}^2/2, we constrain B0B_0 as a function of the spectral index, nBn_B. Using the Planck 2013 likelihood code that uses the Planck temperature and lensing data together with the WMAP 9-year polarization data, we find the 95% upper bounds of B0<0.63B_0<0.63, 0.39, and 0.18~nG for nB=2.9n_B=-2.9, 2.5-2.5, and 1.5-1.5, respectively. For these spectral indices, the optical depth is dominated by dissipation of the decaying MHD turbulence that occurs shortly after the decoupling epoch. Our limits are stronger than the previous limits ignoring the effects of the fields on ionization history. Inverse Compton scattering of CMB photons off electrons in the heated IGM distorts the thermal spectrum of CMB. Our limits on B0B_0 imply that the yy-type distortion from dissipation of fields in the post decoupling era should be smaller than 10910^{-9}, 4×1094\times10^{-9}, and 10910^{-9}, respectively.Comment: 14 pages, 30 figures, calculations revised and updated, accepted for publication in JCA

    Results from the Wilkinson Microwave Anisotropy Probe

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    The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of temperature and polarization over the entire sky in five microwave frequency bands. These full-sky maps were used to obtain measurements of temperature and polarization anisotropy of the cosmic microwave background with the unprecedented accuracy and precision. The analysis of two-point correlation functions of temperature and polarization data gives determinations of the fundamental cosmological parameters such as the age and composition of the universe, as well as the key parameters describing the physics of inflation, which is further constrained by three-point correlation functions. WMAP observations alone reduced the flat Λ\Lambda cold dark matter (Λ\LambdaCDM) cosmological model (six) parameter volume by a factor of >68,000 compared with pre-WMAP measurements. The WMAP observations (sometimes in combination with other astrophysical probes) convincingly show the existence of non-baryonic dark matter, the cosmic neutrino background, flatness of spatial geometry of the universe, a deviation from a scale-invariant spectrum of initial scalar fluctuations, and that the current universe is undergoing an accelerated expansion. The WMAP observations provide the strongest ever support for inflation; namely, the structures we see in the universe originate from quantum fluctuations generated during inflation.Comment: 26 pages, 9 figures, invited review for Special Section "CMB Cosmology" of Progress of Theoretical and Experimental Physics (PTEP). (v2) New ns-r figure added. Accepted for publicatio