Showing papers by "Nabila Aghanim published in 2009"

Cluster scaling relations from cosmological hydrodynamic simulations in a dark-energy dominated universe

Abstract: Context. Clusters are potentially powerful tools for cosmology provided their observed properties, such as the Sunyaev-Zel'dovich (SZ) or X-ray signals, can be translated into physical quantities like mass and temperature. Scaling relations are the appropriate means to perform this translation. It is, therefore, important to understand their evolution and their modifications with respect to the physics and to the underlying cosmology. Aims. In this spirit, we investigate the effect of dark energy on the X-ray and SZ scaling relations. The study is based on the first hydro-simulations of cluster formation for diferent models of dark energy. We present results for four dark-energy models which differ from each other by their equations-of-state parameter, w . Namely, we use a cosmological constant model $w=-1$ (as a reference), a perfect fluid with constant equation of state parameter $w=-0.8$ and one with $w = -1.2$ and a scalar field model (or quintessence) with varying w . Methods. We generate N -body/hydrodynamic simulations that include radiative cooling with the public version of the Hydra code, modified to consider an arbitrary dark-energy component. We produce cluster catalogues for the four models and derive the associated X-ray and SZ scaling relations. Results. We find that dark energy has little effect on scaling laws, making it safe to use the standard Λ CDM scalings for conversion of observed quantities into cluster temperatures and masses.

Biases on the cosmological parameters and thermal Sunyaev–Zel'dovich residuals

Abstract: We examine the biases induced on cosmological parameters when the presence of secondary anisotropies is not taken into account in Cosmic Microwave Background analyses. We first develop an exact analytical expression for computing the biases on parameters when any additive signal is neglected in the analysis. We then apply i t in the context of the forthcoming Planck experiment. For illustration, we investigate the effect of the sole residual thermal Sunyaev‐Zel’dovich signal that remains after cluster extr action. We find in particular that analyses neglecting the presence of this contribution intr oduce on the cosmological parameters ns andτ biases, at least∼ 6.5 and 2.9 times their oneσ confidence intervals. The b parameter is also biased to a lesser extent.

Cross-correlation Study between the Cosmological 21-cm Signal and the kinetic Sunyaev-Zel'dovich effect

Abstract: The Universe's Epoch of Reionization (EoR) can be studied using a number of observational probes that provide complementary or corroborating information. Each of these probes suffers from its own systematic and statistical uncertainties. It is therefore useful to consider the mutual information that these data sets contain. In this paper we present a cross-correlation study between the kinetic Sunyaev-Zel'dovich effect (kSZ) -- produced by the scattering of CMB photons off free electrons produced during the reionization process -- and the cosmological 21cm signal -- which reflects the neutral hydrogen content of the Universe, as a function of redshift. The study is carried out using a simulated reionization history in 100Mpc/h scale N-body simulations with radiative transfer. In essence we find that the two probes anti-correlate. The significance of the anti-correlation signal depends on the extent of the reionization process, wherein extended histories result in a much stronger signal compared to instantaneous cases. Unfortunately however, once the primary CMB fluctuations are included into our simulation they serve as a source of large correlated noise that renders the cross-correlation signal insignificant, regardless of the reionization scenario.

Detectability of the 21 cm-CMB cross-correlation from the EoR

Abstract: The 21-cm line fluctuations and the cosmic microwave background (CMB) are powerful probes of the epoch of reionisation of the universe. We study the potential of the cross-correlation between 21-cm line fluctuations and CMB anisotropy to obtain further constraints on the reionisation history. We compute analytically the 21-cm cross-correlation with the CMB temperature anisotropy and polarisation, and we calculate the signal-to-noise (SN) ratio for its detection with Planck together with LOFAR, MWA and SKA. We find, on the one hand, that the 21-cm cross-correlation signal with CMB polarisation from the instant reionisation can be detected with an SN ratio of $\sim 1$ for LOFAR and $\sim 10$ for SKA. On the other hand, we confirm that the detection of the 21-cm cross-correlation with CMB polarisation is practically infeasible.

Sunyaev-Zel'dovich contribution in CMB analysis

Abstract: The Sunyaev-Zel'dovich (SZ) effect has long been identified as one of the most important secondary effects of the Cosmic Microwave Background (CMB). On the one hand, it is a potentially very powerful cosmological probe providing us with additional constraints and on the other hand it represents the major source of secondary fluctuations at small angular scales (l > 1000). We investigate the effects of the SZ modelling in the determination of the cosmological parameters. We explore the consequences of the SZ power spectrum computation by comparing three increasingly complex modelling, from a fixed template with an amplitude factor to a calculation including the full cosmological parameter dependency. We also examine the dependency of the cosmological parameter estimation on the intra-cluster gas description used to calculate the SZ spectrum. We show that methods assuming an SZ template bias the cosmological parameters (by up to 2 sigmas on sigma_8) when the cosmology used in the template deviates from the reference one. A joint CMB-SZ analysis with a full cosmological dependency of the SZ spectrum does not suffer from such biases and moreover improves the confidence intervals of sigma_8 and Omega_{dm}h^2 (2.5 and 2 times respectively) with respect to a pure CMB analysis. However, the latter method is quite sensitive to the intra-cluster gas parameters and hence requires extra information on the clusters to alleviate the induced biases.