J. V. Arnau

On the microwave background anisotropies produced by nonlinear voids

The Tolman-Bondi solution of the Einstein equations is used to study the microwave background anisotropy produced by a pressureless spherical cosmological inhomogeneity. Our method improves on previous ones because it does not involve any approximating condition and it allows us to assume the following: (1) a general Friedmann-Robertson-Walker background, (2) an arbitrary relative location of the observer and the inhomogeneity, (3) either an overdense or an underdense inhomogeneity with arbitrary size, (4) an arbitrary initial energy density profile, and (5) an arbitrary amplitude of the density contrast

On the Rees-Sciama effect: maps and statistics

Small maps of the Rees–Sciama (RS) effect are simulated by using an appropriate N-body code and a certain ray-tracing procedure. A method designed for the statistical analysis of cosmic microwave background (CMB) maps is applied to study the resulting simulations. These techniques, recently proposed – by our team – to consider lens deformations of the CMB, are adapted to deal with the RS effect. This effect and the deviations from Gaussianity associated to it seem to be too small to be detected in the near future. This conclusion follows from our estimation of both the RS angular power spectrum and the RS reduced n-direction correlation functions for n≤ 6.

Cosmic microwave background anisotropy: deviations from Gaussianity caused by non-linear gravity

Non-linear evolution of cosmological energy density fluctuations triggers deviations from Gaussianity in the temperature distribution of the cosmic microwave background. A method to estimate these deviations is proposed. N-body simulations – in a ΛCDM cosmology – are used to simulate the strongly non-linear evolution of cosmological structures. It is proved that these simulations can be combined with the potential approximation to calculate the statistical moments of the CMB anisotropies produced by non-linear gravity. Some of these moments are computed and the resulting values are different from those corresponding to Gaussianity.

Comparing Rees‐Sciama and Integrated Sachs Wolfe effects

Both the Rees‐Sciama (RS) and the Integrated Sachs‐Wolfe (ISW) effects are produced by the peculiar gravitational potential of cosmological inhomogeneities. This potential fully defines a scalar perturbation of the Robertson‐Walker metric in the longitudinal gauge. The RS (ISW) effect is produced by nonlinear (linear) structures which grow as a result of gravitational instability. The anisotropies corresponding to these two effects are compared for a wide range of angular scales. N‐body simulations and a certain ray‐tracing procedure —recently proposed— are used to study the RS effect.

Looking for the imprints of nonlinear structures on the cosmic microwave background

Many authors have estimated the anisotropies produced by one isolated cosmological non-linear inhomogeneity. This paper is an updated review about these estimates. The main methods used in order to deal with this problem are described. The limitations of these methods are analyzed. Results appear to be particularly interesting in the open non-linear case, in which a general treatment of the anisotropies produced by inhomogeneity distributions is very troublesome. The effects produced by very big structures such as the Great Attractor and the Bootes Void are studied in detail. Some generalities about the origin, detection and features of the Cosmic Microwave Background anisotropies are also presented for the sake of completeness.

The great attractor and the COBE quadrupole

A nonlinear model for the Great Attractor is built. It is based on the Tolman-Bondi solution of the Einstein equations. The angular temperature distribution of the Cosmic Microwave Background produced by the Great Attractor is numerically obtained. Several realizations of the Great Attractor are studied. In all the cases, the distance from the Great Attractor to the Local Group is ≈ 43h−1 Mpc, the density contrast reduces to a half of the central value at a radius of 9h−1 Mpc ⪯ Rc ⪯ 14h−1 Mpc, and the dipole due to the infall towards the inhomogeneity center is 1.33 × 10−3 ⪯ D ⪯ 1.8 × 10−3. A complete arbitrary background is assumed; the density parameter, Σ and the reduced Hubble constant, h, (H = 100h Km s−1 Mpc−1) are 0.2 ⪯ Σ ⪯ 1 and 0.5 ⪯ h ⪯ 1 respectively. The total quadrupole Q is split in two parts, the relativistic Doppler quadrupole, QD, and the reduced quadrupole, Qr, produced by nonlinear gravity. The quadrupoles of the chosen realizations appear to satisfy the following inequalities 5 x 10−7 ⪯ Q ⪯ 12.5 ξ 10−7 and −0.4 ξ 10−7 ⪯ Qr ⪯ 1.6 ξ 10−7; this means that |Qr| ranges from 0.8 % to 3.2 % of the quadrupole Qrms measured by LOBE. Therefore, the subtraction of Qr from Qrms becomes irrelevant.