We study the contribution of a stochastic background (SB) of primordial magnetic fields (PMFs) on the anisotropies in temperature and polarization of the cosmic microwave background (CMB) radiation. ...A SB of PMF modelled as a fully inhomogeneous component induces non-Gaussian scalar, vector and tensor metric linear perturbations. We give the exact expressions for the Fourier spectra of the relevant energy–momentum components of such a SB, given a power-law dependence parametrized by a spectral index nB for the magnetic field power spectrum cut at a damping scale kD. For all the values of nB considered here, the contribution to the CMB temperature pattern by such a SB is dominated by the scalar contribution and then by the vector one at higher multipoles. We also give an analytic estimate of the scalar contribution to the CMB temperature pattern.
The parity symmetry of the cosmic microwave background (CMB) pattern as seen by Wilkinson Microwave Anisotropy Probe 7 yr (WMAP 7 yr) is tested jointly in temperature and polarization at large ...angular scale. A quadratic maximum likelihood (QML) estimator is applied to the WMAP 7-yr low-resolution maps to compute all polarized CMB angular power spectra. The analysis is supported by 10 000 realistic Monte Carlo realizations. We confirm the previously reported parity anomaly for TT in the range δℓ=2, 22 at >99.5 per cent C.L. No anomalies have been detected in TT for a wider ℓ range (up to ℓmax= 40). No violations have been found for EE, TE and BB which we test here for the first time. The cross-spectra TB and EB are found to be consistent with zero. We also forecast Planck capabilities in probing parity violations on low-resolution maps.
The Cold Spot (CS) is a clear feature in the cosmic microwave background (CMB); it could be of primordial origin, or caused by a intervening structure along the line of sight. We identified a large ...projected underdensity in the recently constructed WISE–2MASS all-sky infrared galaxy catalogue aligned with the CS direction at (l, b) ≈ (209°, −57°). It has an angular size of tens of degrees, and shows a ∼20 per cent galaxy underdensity in the centre. Moreover, we find another large underdensity in the projected WISE–2MASS galaxy map at (l, b) ≈ (101°, 46°) (hereafter Draco supervoid), also aligned with a CMB decrement, although less significant than that of the CS direction. Motivated by these findings, we develop spherically symmetric Lemaitre–Tolman–Bondi (LTB) compensated void models to explain the observed CMB decrements with these two underdensities, or ‘supervoids’. Within our perturbative treatment of the LTB voids, we find that the integrated Sachs–Wolfe and Riess–Sciama effects due to the Draco supervoid can account for the CMB decrement observed in the same direction. On the contrary, the extremely deep CMB decrement in the CS direction is more difficult to explain by the presence of the CS supervoid only. Nevertheless, the probability of a random alignment between the CS and the corresponding supervoid is disfavoured, and thus its contribution as a secondary anisotropy cannot be neglected. We comment on how the approximations used in this paper, in particular the assumption of spherical symmetry, could change quantitatively our conclusions and might provide a better explanation for the CMB CS.
We test the hemispherical power asymmetry of the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year low-resolution temperature and polarization maps. We consider two natural estimators for such an ...asymmetry and exploit our implementation of an optimal angular power spectrum estimator for all the six cosmic microwave background spectra. By scanning the whole sky through a sample of 24 directions, we search for asymmetries in the power spectra of the two hemispheres, comparing the results with Monte Carlo simulations drawn from the WMAP 7-year best-fitting model. Our analysis extends previous results to the polarization sector. The level of asymmetry on the internal linear combination temperature map is found to be compatible with previous results, whereas no significant asymmetry on the polarized spectra is detected. We show that our results are only weakly affected by the a posteriori choice of the maximum multipole considered for the analysis. We also forecast the capability to detect dipole modulation by our methodology at Planck sensitivity.
In the context of cosmic microwave background (CMB) data analysis, we compare the efficiency at large scale of two angular power spectrum algorithms, implementing, respectively, the quadratic maximum ...likelihood (QML) estimator and the pseudo-spectrum (pseudo-C
) estimator. By exploiting 1000 realistic Monte Carlo simulations, we find that the QML approach is markedly superior in the range 2 ≤ ≤ 100. At the largest angular scales, e.g. ≤ 10, the variance of the QML is almost 1/3 (1/2) that of the pseudo-C
, when we consider the WMAP kq85 (kq85 enlarged by 8°) mask, making the pseudo-spectrum estimator a very poor option. Even at multipoles 20 ≤ ≤ 60, where pseudo-C
methods are traditionally used to feed the CMB likelihood algorithms, we find an efficiency loss of about 20 per cent, when we considered the WMAP kq85 mask, and of about 15 per cent for the kq85 mask enlarged by 8°. This should be taken into account when claiming accurate results based on pseudo-C
methods. Some examples concerning typical large-scale estimators are provided.
We use a model of polarized Galactic emission developed by the Planck collaboration to assess the impact of foregrounds on B-mode detection at low multipoles. Our main interest is in applications of ...noisy polarization data and in particular in assessing the feasibility of B-mode detection by Planck. This limits the complexity of foreground subtraction techniques that can be applied to the data. We analyse internal linear combination techniques and show that the offset caused by the dominant E-mode polarization pattern leads to a fundamental limit of r∼ 0.1 for the tensor–scalar ratio even in the absence of instrumental noise. We devise a simple, robust, template fitting technique using multifrequency polarization maps. We show that template fitting using Planck data alone offers a feasible way of recovering primordial B-modes from dominant foreground contamination, even in the presence of noise on the data and templates. We implement and test a pixel-based scheme for computing the likelihood function of cosmological parameters at low multipoles that incorporates foreground subtraction of noisy data.
We test the asymmetry of the cosmic microwave background anisotropy jointly in temperature and polarization. We study the hemispherical asymmetry, previously found only in the temperature field, with ...respect to the axis identified by Hansen et al. To this extent, we make use of the low-resolution Wilkinson Microwave Anisotropy Probe 5-yr temperature and polarization Nside= 16 maps and our implementation of an optimal power spectrum estimator. We consider two simple estimators for the power asymmetry and we compare our findings with Monte Carlo simulations which take into account the full noise covariance matrix. We confirm an excess of power in temperature angular power spectrum in the Southern hemisphere at a significant level, between 3 σ and 4 σ depending on the exact range of multipoles considered. We do not find significant power asymmetry in the gradient (curl) component EE (BB) of polarized angular spectra. Furthermore, cross-correlation power spectra, i.e. TE, TB, EB, show no significant hemispherical asymmetry. We also show that the cold spot found by Vielva et al. in the Southern Galactic hemisphere does not alter the significance of the hemispherical asymmetries on multipoles which can be probed by maps at resolution Nside= 16. Although the origin of the hemispherical asymmetry in temperature remains unclear, the study of the polarization pattern could add useful information on its explanation. We therefore forecast by Monte Carlo the Planck capabilities in probing polarization asymmetries.
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