Showing papers by "Nabila Aghanim published in 1998"

Ionization by early quasars and Cosmic Microwave Background anisotropies. (Erratum)

Abstract: The y axis of figure 9, which gives the power amplitude ($l(l+1)C_l$) in units of $10^{-12}$, is incorrectly reported. The correct values are obtained by dividing the amplitudes by 16. All the relative values remain valid, and this therefore does not change the conclusions of the paper.

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

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