arXiv subjects

Fabien Lacasa

Publications and source records attributed to Fabien Lacasa.

22 records · Page 2Linked to original sources

arXiv2014

Non-Gaussianity and extragalactic foregrounds to the Cosmic Microwave Background

[Abridged] This PhD thesis was defended in September 2013 at Université Paris-Sud, France. It studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB). This is particularly important for the analysis of CMB data from the Planck satellite, in which I was involved. I studied in particular the extragalactic foregrounds tracing the Large Scale Structure (LSS) of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). The motivations and summary of this thesis cannot be shortened into the length constraints of this abstract and are thus described in an inner abstract and introduction. In a broad summary, this thesis is organised in the following parts : statistics of random variables and fields, spherical analysis in particular of polyspectra, some cosmology (inflation and its NG, CMB, LSS and halo model), extragalactic foregrounds (tSZ, point-sources), and measuring the NG of these foregrounds with Planck. More specifically and in a disorganised manner, the following were most of my contributions in the field : developments on the effect of masking on the angular bispectrum, introduction of an efficient bispectrum representation, derivation of the bispectrum covariance, generation of non-gaussian simulations, projection of 3D Fourier polyspectra onto 2D spherical ones, treatment of shot-noise terms with the halo model, introduction of a diagrammatic formalism for elegant and simple derivation of galaxy polyspectra, halo model description of the bispectrum of the tSZ effect and of the Cosmic Infrared Background (CIB), phenomenological prescription of the NG of clustered sources and corresponding KSW-like estimator, effect of point-sources NG for Planck, measurement of the CIB bispectrum with Planck data, measurement of the tSZ bispectrum with Planck data and cosmological constraints with it.

astro-ph.CO↗

arXiv2013

Non-Gaussianity of the Cosmic Infrared Background anisotropies II : Predictions of the bispectrum and constraints forecast

Using a full analytical computation of the bispectrum based on the halo model together with the halo occupation number, we derive the bispectrum of the cos- mic infrared background (CIB) anisotropies that trace the clustering of dusty-star- forming galaxies. We focus our analysis on wavelengths in the far-infrared and the sub-millimeter typical of the Planck/HFI and Herschel/SPIRE instruments, 350, 550, 850, and 1380 um. We explore the bispectrum behaviour as a function of several models of evolution of galaxies and show that it is strongly sensitive to that ingredient. Contrary to the power spectrum, the bispectrum, at the four wavelengths, seems dominated by low redshift galaxies. Such a contribution can be hardly limited by applying low flux cuts. We also discuss the contributions of halo mass as a function of the redshift and the wavelength, recovering that each term is sensitive to a different mass range. Furthermore, we show that the CIB bispectrum is a strong contaminant of the Cosmic Microwave Background bispectrum at 850 um and higher. Finally, a Fisher analysis of the power spectrum, bispectrum alone and of the combination of both shows that degeneracies on the HOD parameters are broken by including the bispectrum information, leading to tight constraints even when including foreground residuals.

astro-ph.CO↗

arXiv2013

Non-Gaussianity of the Cosmic Infrared Background anisotropies I : Diagrammatic formalism and application to the angular bispectrum

We present the first halo model based description of the Cosmic Infrared Background (CIB) non-Gaussianity (NG) that is fully parametric. To this end, we introduce, for the first time, a diagrammatic method to compute high order polyspectra of the 3D galaxy density field. It allows an easy derivation and visualisation of the different terms of the polyspectrum. We apply this framework to the power spectrum and bispectrum, and we show how to project them on the celestial sphere in the purpose of the application to the CIB angular anisotropies. Furthermore, we show how to take into account the particular case of the shot noise terms in that framework. Eventually, we compute the CIB angular bispectrum at 857 GHz and study its scale and configuration dependencies, as well as its variations with the halo occupation distribution parameters. Compared to a previously proposed empirical prescription, such physically motivated model is required to describe fully the CIB anisotropies bispectrum. Finally, we compare the CIB bispectrum with the bispectra of other signals potentially present at microwave frequencies, which hints that detection of CIB NG should be possible above 220 GHz.

astro-ph.CO↗

arXiv2012

Non-Gaussianity from extragalactic point-sources

The population of compact extragalactic sources contribute to the non-Gaussianity at Cosmic Microwave Background frequencies. We study their non-Gaussianity using publicly available full-sky simulations. We introduce a parametrisation to visualise efficiently the bispectrum and we describe the scale and frequency dependences of the bispectrum of radio and IR point-sources. We show that the bispectrum is well fitted by an analytical prescription. We find that the clustering of IR sources enhances their non-Gaussianity by several orders of magnitude, and that their bispectrum peaks in the squeezed triangles. Examining the impact of these sources on primordial non-Gaussianity estimation, we find that radio sources yield an important positive bias to local fNL at low frequencies but this bias is efficiently reduced by masking detectable sources. IR sources produce a negative bias at high frequencies, which is not dimmed by the masking, as their clustering is dominated by faint sources.

astro-ph.CO↗