Showing papers by "Nabila Aghanim published in 2004"

The distance duality relation from X-ray and SZ observations of clusters

Abstract: X-ray and Sunyaev-Zel'dovich data of clusters of galaxies enableto construct a test of the distance duality relation between the angular andluminosity distances. We argue that such a test on large cluster samples maybe of importance, as a consistency check, while trying to distinguish betweenvarious models accounting for the acceleration of the universe. The analysisof a data set of 18 clusters shows no significant violation of this relationfor a $\ensuremath{\Lambda}$-ColdDark Matter (CDM) model. The origin and amplitude of systematic effects andthe possibility to increase the precision of this method are discussed.

Detection and discrimination of cosmological non-Gaussian signatures by multi-scale methods

Abstract: Recent Cosmic Microwave Background (CMB) observations indicate that the temperature anisotropies arise from quantum fluctuations in the inflationary scenario. In the simplest inflationary models, the distribution of CMB temperature fluctuations should be Gaussian. However, non-Gaussian signatures can be present. They might have different origins and thus different statistical and morphological characteristics. In this context and motivated by recent and future CMB experiments, we search for, and discriminate between, different non-Gaussian signatures. We analyse simulated maps of three cosmological sources of temperature anisotropies: Gaussian distributed CMB anisotropies from inflation, temperature fluctuations from cosmic strings and anisotropies due to the kinetic Sunyaev-Zel'dovich (SZ) effect both showing a non-Gaussian character. We use different multi-scale methods, namely, wavelet, ridgelet and curvelet transforms. The sensitivity and the discriminating power of the methods is evaluated using simulated data sets. We find that the bi-orthogonal wavelet transform is the most powerful for the detection of non-Gaussian signatures and that the curvelet and ridgelet transforms characterise quite precisely and exclusively the cosmic strings. They allow us thus to detect them in a mixture of CMB + SZ + cosmic strings. We show that not one method only should be applied to understand non-Gaussianity but rather a set of different robust and complementary methods should be used.

Separating the kinetic Sunyaev-Zel'dovich effect from primary cosmic microwave background fluctuations

Abstract: In the present work, we propose a new method aiming at extracting the kinetic Sunyaev-Zel'dovich (KSZ) temper- ature fluctuations embedded in the primary anisotropies of the cosmic microwave background (CMB). We base our study on simulated maps without noise and we consider very simple and minimal assumptions. Our method essentially takes benefit from the spatial correlation between KSZ and the Compton parameter distribution associated with the thermal Sunyaev-Zel'dovich (TSZ) effect of the galaxy clusters; the latter can be obtained by means of multi-frequency based component separation tech- niques. We reconstruct the KSZ signal by interpolating the CMB fluctuations without making any hypothesis other than that the CMB fluctuations are Gaussian distributed. We present two ways of estimating the KSZ fluctuations, after the interpolation step. In the first, we use a blind technique based on canonical Principal Component Analysis, while the second uses a minimi- sation criterion based on the fact that KSZ dominates at small angular scales and that it follows a non-Gaussian distribution. Using the correlation between the input and reconstructed KSZ map we show that the latter can be reconstructed in a very sat- isfactory manner (average correlation coefficient between 0.62 and 0.90), furthermore both the retrieved KSZ power spectrum and temperature fluctuation distribution are in quite good agreement with the original signal. The ratio between the input and reconstructed power spectrum is indeed very close to one up to a multipole � ∼ 200 in the best case. The method presented here can be considered as a promising starting point to identify in CMB observations the temperature fluctuation associated with the KSZ effect.

Large Scale Magnetogenesis Through Radiation Pressure

Abstract: We present a new model for the generation of magnetic fields on large scales occurring at the end of cosmological reionisation. The inhomogeneous radiation provided by luminous sources and the fluctuations in the matter density field are the major ingredients of the model. More specifically, differential radiation pressure acting on ions and electrons gives rise to electric currents which induce magnetic fields on large scales. We show that on protogalactic scales, this process is highly efficient, leading to magnetic field amplitudes of the order of Gauss. While remaining of negligible dynamical impact, those amplitudes are million times higher than those obtained in usual astrophysical magnetogenesis models. Finally, we derive the relation between the power spectrum of the generated field and the one of the matter density fluctuations. We show in particular that magnetic fields are preferably created on large (galactic or cluster) scales. Small scale magnetic fields are strongly disfavoured, which further makes the process we propose an ideal candidate to explain the origin of magnetic fields in large scale structures.

Primordial quadrupole-induced polarisation from filamentary structures and galaxy clusters

Abstract: We present the first computation of the Cosmic Microwave Background (CMB) polarisation power spectrum from galaxy clusters and filaments using hydrodynamical simulations of large scale structure. We give the $E$ and $B$ mode power spectra of the CMB quadrupole induced polarisation between $\ell \sim 560$ and 20000. We find that the contribution from warm ionised gas in filamentary structures dominates the polarised signal from galaxy clusters by more than one order of magnitude on large scales (below $\ell \sim 1000$) and by a factor of about two on small scales ($\ell \gsim 10000$). We study the dependence of the power spectra with $\sigma_8$. Assuming the power spectra vary like $\sigma_8^n$ we find $n=3.2-4.0$ for filaments and $n=3.5-4.6$ for clusters.