Showing papers by "Simon Prunet published in 1998"

Moving gravitational lenses: imprints on the cosmic microwave background

Abstract: With the new generation of instruments for Cosmic Microwave Background (CMB) observations aiming at an ac- curacy level of a few percent in the measurement of the angular power spectrum of the anisotropies, the study of the contribu- tions due to secondary effects has gained impetus. Furthermore, a reinvestigation of the main secondary effects is crucial in order to predict and quantify their effects on the CMB and the errors that they induce in the measurements. In this paper, we investigate the contribution, to the CMB, of secondary anisotropies induced by the transverse motions of clusters of galaxies. This effect is similar to the Kaiser-Stebbins effect. In order to address this problem, we model the gravita- tional potential well of an individual structure using the Navarro, Frenk & White profile. We generalise the effect of one structure to a population of objects predicted using the Press-Schechter formalism. We simulate maps of these secondary fluctuations, compute the angular power spectrum and derive the average contributions for three cosmological models. We then investi- gate a simple method to separate this new contribution from the primary anisotropies and from the main secondary effect, the Sunyaev-Zel'dovich kinetic effect from the lensing clusters. directly related to the initial density perturbations which are the progenitors to the cosmic structures (galaxies and galaxies clus- ters) in the present universe; but which are first and foremost the relics of the very early initial conditions of the universe. Between recombination and the present time, the CMB pho- tons could have undergone various interactions with the matter and structures present along their lines of sight. Some of these in- teractions can induce additional temperature fluctuations called, secondary anisotropies because they are generated after the re- combination. Along a line of sight, one measures temperature fluctuations which are the superposition of the primary and sec- ondary anisotropies. As a result, and in the context of the future CMB experiments, accurate analysis of the data will be needed in order to account for the foreground contributions due to the secondary fluctuations. Photon-matter interactions between re- combination and the present time are due to the presence of ionised matter or to variations of the gravitational potential wells along the lines of sight. The CMB photons interact with the ionised matter mainly through Compton interactions. In fact, after recombination the universe could have been re-ionised globally or locally. Global early re-ionisation has been widely studied (see Dodelson & Jubas 1995 for a recent review and references therein). Its main effect is to either smooth or wipe out some of the primary anisotropies; but the interactions of the photons with the mat- ter in a fully ionised universe can also give rise to secondary anisotropies through the Vishniac effect (Vishniac 1987). This second order effect has maximum amplitudes for a very early re-ionisation. The case of a late inhomogeneous re-ionisation and its imprints on the CMB fluctuations has been investigated (Aghanim et al. 1996) and found to be rather important. In this case, the secondary anisotropies are due to the bulk mo- tion of ionised clouds with respect to the CMB frame. When the re-ionisation is localised in hot ionised intra-cluster me- dia the photons interact with the free electrons. The inverse Compton scattering between photons and electrons leads to the so-called Sunyaev-Zel'dovich (hereafter SZ) effect (Sunyaev & Zel'dovich1972, 1980). The Compton distortion due to the mo- tion of the electrons in the gas is called the thermal SZ effect. The kinetic SZ effect is a Doppler distortion due to the pecu- liar bulk motion of the cluster with respect to the Hubble flow. The SZ thermal effect has the unique property of depressing the

Galactic dust polarized emission at high latitudes and cmb polarization

Abstract: With recent instrumental advances, it might become possible to measure the polarization of the Cosmic Microwave Background (CMB), e.g. by future space missions like MAP and Planck Surveyor. In this paper, we estimate the dust po- larized emission in our galaxy which is the major foreground to cope with for measuring the CMB polarization in the Wien part of CMB spectrum. We model the dust polarized emission in the galaxy using the three-dimensional HI maps of the Lei- den/Dwingeloo survey at high galactic latitudes. We use the fact that the dust emission, for a wide range of wavelengths, has a tight correlation with the HI emission maps of this survey (Boulanger et al. 1996). Assuming the dust grains to be oblate with axis ratio ' 2=3, which recent studies support, we deter- mine the intrinsic dust polarized emissivity. The distribution of magnetic field with respect to the dust grain distribution is quite uncertain, we thus consider three extreme cases: (1) The mag- netic field is aligned with the major axis of the dust structure, (2) the magnetic field has a random direction in the plane perpen- dicular to the direction of major axis of the dust structure, and (3) the magnetic field is unidirectional throughout. We further assume, as recent observations and theoretical analyses support, that the dust grains align with the magnetic field independently of its strength. The polarization reduction factor from misalign- ment of the direction of polarization from the plane of the sky and the differential polarization along a line of sight is calcu- lated using these maps, to construct two-dimensional maps of dust polarized emission. We calculate the angular power spec- trum of dust polarized emission from these maps and cast it in variables which allow a direct comparison with the polarized component of the CMB. Our results, at frequencies ' 100GHz, suggest that: (a) This foreground contamination is smaller than the scalar-induced polarization of the CMB at ' > 200 while

Galactic dust polarized emission at high latitudes and CMB polarization

Abstract: We estimate the dust polarized emission in our galaxy at high galactic latitudes, which is the dominant foreground for measuring CMB polarization using the high frequency instrument (HFI) aboard Planck surveyor. We compare it with the level of CMB polarization and conclude that, for angular scales $\le 1^{\circ}$, the scalar-induced CMB polarization and temperature-polarization cross-correlation are much larger than the foreground level at $ u \simeq 100 GHz$. The tensor-induced signals seem to be at best comparable to the foreground level.}

Parameters extraction by Planck for a CDM model with BSI steplike primordial spectrum and cosmological constant

Abstract: We consider a class of spatially flat cold dark matter (CDM) models, with a cosmological constant and a broken-scale-invariant (BSI) steplike primordial spectrum of adiabatic perturbations, previously found to be in very good agreement with observations. Performing a Fisher matrix analysis, we show that in case of a large gravitational waves (GW) contribution some free parameters (defining the step) of our BSI model can be extracted with remarkable accuracy by the Planck satellite, thanks to the polarisation anisotropy measurements. Further, cosmological parameters can still be found with very good precision, despite a larger number of free parameters than in the simplest inflationary models.

Multi-frequency Wiener filtering of CMB data with polarisation

Abstract: One goal of CMB data analysis is to combine data at different frequencies, angular resolutions, and noise levels in order to best extract the component with a Plankian spectral behaviour. A multi-frequency Wiener filtering method has been proposed in this context by Bouchet, Gispert and Puget (1995) and in parallel by Tegmark and Efstathiou (1996). As shown in Bouchet and Gispert (1998a), this linear method is also convenient to estimate a priori, given a sky model and an experimental description, the residual errors on the CMB power spectrum assuming the foregrounds have been removed with this method. In this paper, we extend the method to the case when additional polarisation data is available. In particular, we derive the errors on the power spectra involving polarisation and show numerical results for the specifications of the future CMB space missions MAP and \plancks \footnote{For current noise specifications and angular and frequency coverage of these experiments, see this http URL and this http URL} when it is assumed that the Galactic synchrotron and dust emission are respectively about 40% and 10 % polarised. We consider two underlying models for our study: we take a standard CDM model with $\tau = 0.1$ for the extraction of $E$-mode polarisation and $ET$ cross-correlation ; for $B$-mode polarisation we consider a tilted CDM model with $n_s = 0.9, n_T = -0.1$ and $T/S = 0.7$.

Moving gravitational lenses: Imprints on the CMB

Abstract: . With the new generation of instruments forCosmic Microwave Background (CMB) observations aim-ing at an accuracy level of a few percent in the measure-ment of the angular power spectrum of the anisotropies,the study of the contributions due to secondary effectshas gained impetus. Furthermore, a reinvestigation of themain secondary effects is crucial in order to predict andquantify their effects on the CMB and the errors that theyinduce in the measurements.In this paper, we investigate the contribution, to theCMB, of secondary anisotropies induced by the transversemotions of clusters of galaxies. This effect is similar to theKaiser–Stebbins effect. In order to address this problem,we model the gravitational potential well of an individ-ual structure using the Navarro, Frenk & White profile.We generalise the effect of one structure to a populationof objects predicted using the Press-Schechter formalism.We simulate maps of these secondary fluctuations, com-pute the angular power spectrum and derive the averagecontributions for three cosmological models. We then in-vestigate a simple method to separate this new contribu-tion from the primary anisotropies and from the main sec-ondary effect, the Sunyaev-Zel’dovich kinetic effect fromthe lensing clusters.Key words:Cosmology: cosmic microwave background –gravitational lensing – secondary fluctuations – clusters ofgalaxies1. IntroductionDuring the next decade, several experiments are plannedto observe the Cosmic MicrowaveBackground (CMB) andmeasure its temperature fluctuations (Planck surveyor,Map, Boomerang, ...). Their challenge is to measure thesmall scales anisotropies of the CMB (a few arcminutesup to ten degrees scale) with sensitivities better by afactor 10 than the COBE satellite (Smoot et al. 1992).These high sensitivity and resolution measurements will