F. Argüeso

The performance of spherical wavelets to detect non-Gaussianity in the cosmic microwave background sky

We investigate the performance of spherical wavelets in discriminating between standard inflationary (Gaussian) and non-Gaussian models. For the latter we consider small perturbations of the Gaussian model in which an artificially specified skewness or kurtosis is introduced through the Edgeworth expansion. By combining all the information present in all the wavelet scales with the Fisher discriminant, we find that the spherical Mexican Hat wavelets are clearly superior to the spherical Haar wavelets. The former can detect levels of skewness and kurtosis of ≈1 per cent for 33-arcmin resolution, an order of magnitude smaller than the latter. Also, as expected, both wavelets are better for discriminating between the models than the direct consideration of moments of the temperature maps. The introduction of instrumental white noise in the maps, S/N = 1, does not change the main results of this paper.

The Mexican hat wavelet family: application to point-source detection in cosmic microwave background maps

We propose a detection technique in 2D images based on an isotropic wavelet family. This family is naturally constructed as an extension of the Gaussian-Mexican Hat Wavelet pair and for that reason we call it the Mexican Hat Wavelet Family (MHWF). We show the performance of these wavelets for dealing with the detection of point extragalactic sources in cosmic microwave background (CMB) maps: a very important issue within the most general problem of the component separation of the microwave sky. In particular, simulations for one channel (44 GHz) of the forthcoming Planck mission have been analysed. We present the results and compare them with those obtained using the Mexican Hat Wavelet technique (MHW), which has been proven a suitable tool for detecting point sources. The MHWF provides a point source catalogue at 44 GHz of 690 sources. Under the same conditions, the MHW provides 604 sources.

Spherical Mexican hat wavelet: an application to detect non‐Gaussianity in the COBE‐DMR maps

ABSTRA C T The spherical Mexican hat wavelet is introduced in this paper, with the aim of testing the Gaussianity of the cosmic microwave background temperature fluctuations. Using the information given by the wavelet coefficients at several scales, we have performed several statistical tests on the COBE-DMR maps to search for evidence of non-Gaussianity. Skewness, kurtosis, scale ‐ scale correlations (for two and three scales) and Kolmogorov‐ Smirnov tests indicate that the COBE-DMR data are consistent with a Gaussian distribution. We have extended the analysis to compare temperature values provided by COBE-DMR data with distributions (obtained from Gaussian simulations) at each pixel and at each scale. The number of pixels with temperature values outside the 95 and 99 per cent limits is consistent with that obtained from Gaussian simulations, at all scales. Moreover, the extrema values for COBE-DMR data (maximum and minimum temperatures in the map) are also consistent with those obtained from Gaussian simulations.

Comparison of filters for the detection of point sources in Planck simulations

We study the detection of extragalactic point sources in 2D flat simulations for all the frequencies of the forthcoming ESA’s Planck mission. In this work, we have used the most recent available templates of the microwave sky: as for the diffuse Galactic components and the Sunyaev‐Zel’dovich clusters we have used the ‘Plank Reference Sky Model’; as for the extragalactic point sources, our simulations ‐ which comprise all the source populations relevant in this frequency interval ‐ are based on up-to-date cosmological evolution models for sources. To consistently compare the capabilities of different filters for the compilation of ‐ hopefully ‐ the most complete blind catalogue of point sources, we have obtained three catalogues by filtering the simulated sky maps with: the matched filter (MF), the Mexican Hat Wavelet (MHW1) and the Mexican Hat Wavelet 2 (MHW2), the first two members of the Mexican Hat Wavelet Family. For the nine Planck frequencies we show the number of real and spurious detections and the percentage of spurious detections at different flux detection limits as well as the completeness level of the catalogues and the average errors in the estimation of the flux density of detected sources. Allowing a 5 per cent of spurious detections, we obtain the following number of detections by filtering with the MHW2 an area equivalent to half of the sky: 580 (30 GHz), 342 (44 GHz), 341 (70 GHz), 730 (100 GHz), 1130 (143 GHz), 1233 (217 GHz), 990 (353 GHz), 1025 (545 GHz) and 3183 (857 GHz). Our current results indicate that the MF and the MHW2 yield similar results, whereas the MHW1 performs worse in some cases and especially at very low fluxes. This is a relevant result, because we are able to obtain comparable results with the well-known MF and with this specific wavelet, the MHW2, which is much easier to implement and use.

Predictions of the Angular Power Spectrum of Clustered Extragalactic Point Sources at Cosmic Microwave Background Frequencies from Flat and All-Sky Two-dimensional Simulations

We present predictions of the angular power spectrum of cosmic microwave background (CMB) fluctuations due to extragalactic point sources (EPSs) by using a method for simulating realistic two-dimensional distributions of clustered EPSs. Both radio- and far-IR-selected source populations are taken into account. To analyze different clustering scenarios, we exploit the angular power spectra of EPSs, P(k), estimated either by data coming from currently available surveys or by means of theoretical predictions. By adopting the source number counts predicted by the Toffolatti et al. evolution model, capable of accounting well for the available data at radio (centimeter) wavelengths, we are able to reproduce current data on the two-point angular correlation functions, w(?), of radio sources. We can confirm that the detection of primordial CMB anisotropies is not hampered by undetected clustered sources at frequencies ?150-200 GHz. On the other hand, our current findings show that at higher frequencies the clustering signal could severely reduce the detectability of intrinsic CMB anisotropies, thus confirming previous theoretical predictions. We also show that unsubtracted EPSs can account for the excess signal at high multipoles detected by recent CMB anisotropy experiments. Moreover, the additional power due to the clustering of sources gives rise to a small but nonnegligible contribution to the same excess signal. As a final result, we also present an example of a currently feasible realistic map of EPSs at 70 GHz, by taking into account data on bright detected sources, as well as the previously quoted model for number counts. Eventually, these simulated sky maps could prove very useful for testing the efficiency of component separation techniques, the capability of new algorithms for the detection of EPSs, and the appearance of non-Gaussian signatures in residue CMB maps, in the presence of sources that are not Poisson-distributed in the sky.

COBE–DMR constraints on the non‐linear coupling parameter: a wavelet based method

Non-linearity introduced in slow-roll inflation will produce weakly non-Gaussian cosmic microwave background (CMB) temperature fluctuations. We have simulated non-Gaussian large-scale CMB maps (including COBE-DMR constraints) introducing an additional quadratic term in the gravitational potential. The amount of non-linearity is controlled by the so-called non-linear coupling parameter f n l . An analysis based on the Spherical Mexican Hat wavelet was applied to these and to the COBE-DMR maps. Skewness values obtained at several scales were combined into a Fisher discriminant. Comparison of the Fisher discriminant distributions obtained for different non-linear coupling parameters with the COBE-DMR values sets a constraint of ‖ f n l ‖ < 1100 at the 68 per cent confidence level. This new constraint is tighter than the one previously obtained by using the bispectrum by Komatsu et al.

Contributions of Point Extragalactic Sources to the Cosmic Microwave Background Bispectrum

All the analyses of cosmic microwave background (CMB) temperature maps up to date show that CMB anisotropies follow a Gaussian distribution. On the other hand, astrophysical foregrounds, which hamper the detection of the CMB angular power spectrum, are not Gaussian-distributed on the sky. Therefore, they should give a sizeable contribution to the CMB bispectrum. In fact, the first-year data of the Wilkinson Microwave Anisotropy Probe (WMAP) mission have allowed the first detection of the extragalactic source contribution to the CMB bispectrum at 41 GHz and, at the same time, much tighter limits than before to non-Gaussian primordial fluctuations. In view of the above, and for achieving higher precision in current and future CMB measurements of non-Gaussianity, in this paper we discuss a comprehensive assessment of the bispectrum due to either uncorrelated or clustered extragalactic point sources in the entire frequency interval around the CMB intensity peak. Our calculations, based on current cosmological evolution models for sources, show that the reduced angular bispectrum due to point sources bps should be detectable in all WMAP and Planck frequency channels. We also find agreement with the results for bps at 41 GHz coming from the analysis of the first-year WMAP data. Moreover, by comparing bps with the primordial reduced CMB bispectrum, we find that only the peak value of the primordial bispectrum (which appears at l 200) results in greater than bps in a frequency window around the intensity peak of the CMB. The amplitude of this window basically depends on the capability of the source detection algorithms (i.e., on the achievable flux detection limit Slim for sources). Finally, our current results show that at low frequencies (i.e., ν ≤ 100 GHz) the angular bispectrum of a clustered distribution of sources does not seem substantially different from that of Poisson-distributed ones, by using realistic angular correlation functions suitable to apply to the relevant source populations. On the other hand, we also find that at higher frequencies (i.e., ν ≥ 300 GHz) the clustering term can greatly enhance the normalization of bps.

Predictions on the angular power spectrum of clustered extragalactic point sources at CMB frequencies from flat and all--sky 2D-simulations

We present predictions of the angular power spectrum of cosmic microwave background (CMB) fluctuations due to extragalactic point sources (EPSs) by using a method for simulating realistic two-dimensional distributions of clustered EPSs. Both radio- and far-IR-selected source populations are taken into account. To analyze different clustering scenarios, we exploit the angular power spectra of EPSs, P(k), estimated either by data coming from currently available surveys or by means of theoretical predictions. By adopting the source number counts predicted by the Toffolatti et al. evolution model, capable of accounting well for the available data at radio (centimeter) wavelengths, we are able to reproduce current data on the two-point angular correlation functions, w(?), of radio sources. We can confirm that the detection of primordial CMB anisotropies is not hampered by undetected clustered sources at frequencies ?150-200 GHz. On the other hand, our current findings show that at higher frequencies the clustering signal could severely reduce the detectability of intrinsic CMB anisotropies, thus confirming previous theoretical predictions. We also show that unsubtracted EPSs can account for the excess signal at high multipoles detected by recent CMB anisotropy experiments. Moreover, the additional power due to the clustering of sources gives rise to a small but nonnegligible contribution to the same excess signal. As a final result, we also present an example of a currently feasible realistic map of EPSs at 70 GHz, by taking into account data on bright detected sources, as well as the previously quoted model for number counts. Eventually, these simulated sky maps could prove very useful for testing the efficiency of component separation techniques, the capability of new algorithms for the detection of EPSs, and the appearance of non-Gaussian signatures in residue CMB maps, in the presence of sources that are not Poisson-distributed in the sky.

Extragalactic source contributions to arcminute-scale Cosmic Microwave Background anisotropies

The possible contributions of the various classes of extragalactic sources (including, in addition to the canonical radio sources, GHz Peaked Spectrum sources, advection-dominated sources, starburst galaxies, high-redshift proto-spheroidal galaxies) to the arcminute scale fluctuations measured by the CBI, BIMA, and ACBAR experiments are discussed. At 30 GHz, fluctuations due to radio sources undetected by ancillary low-frequency surveys may be higher than estimated by the CBI and BIMA groups. High-redshift dusty galaxies, whose fluctuations may be strongly enhanced by the effect of clustering, could contribute to the BIMA excess signal, and dominate at 150 GHz (the ACBAR frequency). Moreover, in the present data situation, the dust emission of these high-redshift sources set an unavoidable limit to the detection of primordial CMB anisotropies at high multipoles, even at frequencies as low as

The Planck Surveyor mission: astrophysical prospects

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