Non-Gaussianity in CMB analysis: bispectrum estimation and foreground subtraction

The focus of this work is the development of statistical and numerical methods forthe study of non-Gaussian and/or anisotropic features in cosmological surveys of themicrowave sky. We focus on two very different types of non-Gaussian (NG) signals. The former is primordial non-Gaussianity (PNG), generated in the very Early Universeduring the inflationary expansion stage. In this case the aim of our study will be that ofexploiting the NG component in order to extract useful cosmological information. The latter is non-Gaussianity generated by astrophysical foreground contamination. In thiscase, the goal is instead that of using non-Gaussianity as a tool to help in removingthese spurious, non-cosmological components (of course foregrounds themselves contain relevant astrophysical information, but the focus in this thesis is on Cosmology, thereforeforegrounds are regarded here only as a contaminant). Considerable efforts have been put so far in the search for deviations from Gaussianity in the CMB anisotropies, that are expected to provide invaluable information aboutthe Inflationary epoch. Inflation is in fact expected to produce an isotropic and nearly-Gaussian fluctuation field. However, a large amount of models also predicts very small,but highly model dependent NG signatures. This is the main reason behind the largeinterest in primordial NG studies. Of course, the pursuit for primordial non-Gaussianity must rely on beyond power spectrum statistics. It turns out that the most important higher order correlator produced by interactions during Inflation is the three pointfunction, or, more precisely, its Fourier space counterpart, called the bispectrum. Toovercome the issue of computing the full bispectrum of the observed field, that would require a prohibitive amount of computational time, the search for PNG features is carriedout by fitting theoretically motivated bispectrum templates to the data. Among those, one can find bispectrum templates with a scale-dependent (SD) bispectrum amplitude. Such templates have actually received little attention so far in the literature, especiallyas long as NG statistical estimation and data analysis are concerned. This is why a significant part of this thesis will be devoted to the development and application of efficientstatistical pipelines for CMB scale-dependent bispectra estimation. We present here theresults of the estimation of several primordial running bispectra obtained from WMAP9 year and Planck data-set. iiiThe second part of this thesis deals instead, as mentioned iin the beginning, withthe component separation problem, i.e. the identification of the different sources thatcontributes to the microwave sky brightness. Foreground emission produces several,potentially large, non-Gaussian signatures that can in principle be used to identify andremove the spurious components from the microwave sky maps. Our focus will be onthe development of a foreground cleaning technique relying on the hypothesis that, ifthe data are represented in a proper basis, the foreground signal is sparse. Sparsenessimplies that the majority of the signal is concentrated in few basis elements, that can be used to fit the corresponding component with a thresholding algorithm. We verifythat the spherical needlet frame has the right properties to disentangle the coherentforeground emission from the isotropic stochastic CMB signal. We will make clear inthe following how sparseness in needlet space is actually in several ways linked to thecoherence, anisotropy and non-Gaussianity of the foreground components.. The mainadvantages of our needlet thresholding technique are that it does not requires multi-frequency information as well as that it can be used in combination with other methods. Therefore it can represent a valuable tool in experiments with limited frequency coverage,as current ground-based CMB surveys

The integrated angular bispectrum

We study the position-dependent power spectrum and the integrated bispectrum statistic for 2D cosmological fields on the sphere (integrated angular bispectrum). First, we derive a useful, $m$-independent, formula for the full-sky integrated angular bispectrum, based on the construction of azimuthally symmetric patches. We then implement a pipeline for integrated angular bispectrum estimation, including a mean-field correction to account for spurious isotropy-breaking effects in realistic conditions (e.g., inhomogenous noise, sky masking). Finally, we show examples of applications of this estimator to CMB analysis, both using simulations and actual Planck data. Such examples include $f_\mathrm{NL}$ estimation, analyses of non-Gaussianity from secondary anisotropies (ISW-lensing and ISW-tSZ-tSZ bispectra) and studies of non-Gaussian signatures from foreground contamination.Comment: 38 pages, 14 figure

CHEX-MATE: pressure profiles of 6 galaxy clusters as seen by SPT and Planck

Pressure profiles are sensitive probes of the thermodynamic conditions and the internal structure of galaxy clusters. The intra-cluster gas resides in hydrostatic equilibrium within the Dark Matter gravitational potential. However, this equilibrium may be perturbed, e.g. as a consequence of thermal energy losses, feedback and non-thermal pressure supports. Accurate measures of the gas pressure over the cosmic times are crucial to constrain the cluster evolution as well as the contribution of astrophysical processes. In this work we presented a novel algorithm to derive the pressure profiles of galaxy clusters from the Sunyaev-Zeldovich (SZ) signal measured on a combination of Planck and South Pole Telescope (SPT) observations. The synergy of the two instruments made it possible to track the profiles on a wide range of spatial scales. We exploited the sensitivity to the larger scales of the Planck High-Frequency Instrument to observe the faint peripheries, and the higher spatial resolution of SPT to solve the innermost regions. We developed a two-step pipeline to take advantage of the specifications of each instrument. We first performed a component separation on the two data-sets separately to remove the background (CMB) and foreground (galactic emission) contaminants. Then we jointly fitted a parametric pressure profile model on a combination of Planck and SPT data. We validated our technique on a sample of 6 CHEX-MATE clusters detected by SPT. We compare the results of the SZ analysis with profiles derived from X-ray observations with XMM-Newton. We find an excellent agreement between these two independent probes of the gas pressure structure.Comment: 19 pages, 13 figures, submitted to A&

Non-Gaussianity in CMB analysis: bispectrum estimation and foreground subtraction

The focus of this work is the development of statistical and numerical methods forthe study of non-Gaussian and/or anisotropic features in cosmological surveys of themicrowave sky. We focus on two very different types of non-Gaussian (NG) signals. The former is primordial non-Gaussianity (PNG), generated in the very Early Universeduring the inflationary expansion stage. In this case the aim of our study will be that ofexploiting the NG component in order to extract useful cosmological information. The latter is non-Gaussianity generated by astrophysical foreground contamination. In thiscase, the goal is instead that of using non-Gaussianity as a tool to help in removingthese spurious, non-cosmological components (of course foregrounds themselves contain relevant astrophysical information, but the focus in this thesis is on Cosmology, thereforeforegrounds are regarded here only as a contaminant). Considerable efforts have been put so far in the search for deviations from Gaussianity in the CMB anisotropies, that are expected to provide invaluable information aboutthe Inflationary epoch. Inflation is in fact expected to produce an isotropic and nearly-Gaussian fluctuation field. However, a large amount of models also predicts very small,but highly model dependent NG signatures. This is the main reason behind the largeinterest in primordial NG studies. Of course, the pursuit for primordial non-Gaussianity must rely on beyond power spectrum statistics. It turns out that the most important higher order correlator produced by interactions during Inflation is the three pointfunction, or, more precisely, its Fourier space counterpart, called the bispectrum. Toovercome the issue of computing the full bispectrum of the observed field, that would require a prohibitive amount of computational time, the search for PNG features is carriedout by fitting theoretically motivated bispectrum templates to the data. Among those, one can find bispectrum templates with a scale-dependent (SD) bispectrum amplitude. Such templates have actually received little attention so far in the literature, especiallyas long as NG statistical estimation and data analysis are concerned. This is why a significant part of this thesis will be devoted to the development and application of efficientstatistical pipelines for CMB scale-dependent bispectra estimation. We present here theresults of the estimation of several primordial running bispectra obtained from WMAP9 year and Planck data-set. iiiThe second part of this thesis deals instead, as mentioned iin the beginning, withthe component separation problem, i.e. the identification of the different sources thatcontributes to the microwave sky brightness. Foreground emission produces several,potentially large, non-Gaussian signatures that can in principle be used to identify andremove the spurious components from the microwave sky maps. Our focus will be onthe development of a foreground cleaning technique relying on the hypothesis that, ifthe data are represented in a proper basis, the foreground signal is sparse. Sparsenessimplies that the majority of the signal is concentrated in few basis elements, that can be used to fit the corresponding component with a thresholding algorithm. We verifythat the spherical needlet frame has the right properties to disentangle the coherentforeground emission from the isotropic stochastic CMB signal. We will make clear inthe following how sparseness in needlet space is actually in several ways linked to thecoherence, anisotropy and non-Gaussianity of the foreground components.. The mainadvantages of our needlet thresholding technique are that it does not requires multi-frequency information as well as that it can be used in combination with other methods. Therefore it can represent a valuable tool in experiments with limited frequency coverage,as current ground-based CMB surveys.l tema centrale di questa tesi `e lo sviluppo di metodi statistici e numerici per lo studio di caratteristiche non gaussiane e/o anisotrope in esperimenti mirati alla misura dellaradiazione cosmica di fondo (CMB, dall’inglese Cosmic Microwave Background). Ciconcentriamo su due tipi molto diversi di segnali non gaussiani: il primo `e la non Gaussianit`a primordiale, che si ipotizza venga generata nell’Universo primordiale durante l’epoca inflazionaria. Lo studio di questo tipo di non-Gaussianit`a permette di ottenere preziose informazioni cosmologiche. Il secondo `e invece la non-Gaussianit`a generata dalla contaminazione dovuta al foreground astrofisico. In questo caso, invece, il nostroobiettivo `e utilizzare la non-Gaussianit`a come tracciante per identificare e rimuovere lecomponenti spurie non cosmologiche (ovviamente l’emissione di foreground contiene informazioni astrofisiche rilevanti, ma il tema di questa tesi verte sulla cosmologia, quindi verra' considerata solo in virtu' dell’effetto contaminante in esperimenti che mirano a ricostruire la CMB). Sforzi considerevoli sono stati spesi finora nel tentativo di misurare piccole deviazionidalla Gaussianita' nelle anisotropie della CMB, che fornirebbero informazioni inestimabilisull’epoca dell’Inflazione. La teoria prevede che l’Inflazione produca un campo di fluttuazioni isotropo e quasi Gaussiano. Tuttavia, una grande quantit`a di modelli prevede anche l’insorgenza di piccole componenti non Gaussiane, le cui caratteristiche dipendono fortemente dal modello inflazionario sottostante. Questa `e la ragione principaledel grande interesse della comunit`a cosmologica per la misura della non Gaussianita'. Naturalmente, nella ricerca della non-Gaussianit`a primordiale `e necessario ricorrere astatistiche di ordine superiore rispetto allo spettro di potenza. Ci si aspetta che la maggior parte del segnale non Gaussiano prodotto durante l’Inflazione si presenti sotto formadi correlazioni a tre punti, che possono essere misurate nello spazio armonico dal bispettro. Purtroppo, a causa dell’elevato tempo computazionale richiesto, non `e possibile calcolare direttamente il bispettro dai dati. La ricerca di segnali non gaussiani consiste quindi nel misurare la correlazione tra il bispettro dei dati e determinati modelli teorici che riproducono il segnale predetto da specifici modelli inflazionari. Molte teorie inflazionarie producono correlazioni ad alto ordine il cui bispettro presenta un ampiezza dipendente dalla scala. Questo `e il motivo per cui una parte significativa di questa tesi sara' dedicata allo sviluppo di tecniche statistiche per la stima di bispettri con un esplicita dipendenza dalla scala in osservazioni della CMB. I risultati presentati in questa tesi sono ottenuti dalle osservazioni dei satelliti WMAP e Planck. La seconda parte di questo lavoro riguarda invece il problema dell’identificazione dellediverse fonti che contribuiscono alla luminosit`a del cielo nelle frequenze delle microonde. L’emissione di foreground potenzialmente produce grandi deviazioni dalla Gaussianita, che in linea di principio possono essere utilizzate per identificare e rimuovere i componenti spuri dalle mappe del cielo a microonde. Il nostro obiettivo `e lo sviluppo di una tecnica di pulizia dai foreground basata sull’ipotesi che, se i dati vengono rappresentati nella base appropriata, il segnale delle emissioni di foreground appare sparso. La sparsit`a implica che la maggior parte del segnale sia concentrata in pochi elementi della base, che possono essere usati per ricostruire il componente corrispondente ricorrendo a una tecnica detta thresholding. Abbiamo verificato che il frame delle needlet sferiche ha le propriet`a ideali per separare il segnale coerente del foreground dal segnale isotropo e stocastico della CMB. I principali vantaggi della nostra tecnica di needlet thresholding sono, in primo luogo, che non richiede di avere osservazioni a diverse frequenze e inoltre che pu`o essere utilizzata in combinazione con altri metodi. Pertanto pu`o essere uno strumento prezioso in esperimenti che osservano il cielo in un limitato intervallo di frequenza come, per esempio, gli attuali esperimenti che mirano a misurare la CMB da terra

Primordial non-Gaussianity and scale-dependent bispectra in the Cosmic Microwave Background

The measurement of a primordial non-gaussian signal in the CMB temperature distribution is the best way to discriminate between different inflationary model. We develop a scale dependent factorizable form for the CMB bispectra, and a complete set of analytical tools to compute scale dependent bispectra and perform analysis and forecast for the non-gaussian amplitude parameter fNL and for the running parameter nNG

Pressure profiles of distant Galaxy clusters with

We present a full set of numerical tools to extract Galaxy Cluster pressure profiles from the joint analysis of Planck and South Pole Telescope (SPT) observations. Pressure profiles are powerful tracers of the thermodynamic properties and the internal structure of the clusters. Tracing the pressure over the cosmic times allows one to constraints the evolution of the cluster structure and the contribution of astrophysical phenomena. SPT and Planck are complementary to constrain the cluster structure at various spatial scales. The SPT cluster catalogue counts 677 cluster candidates up to redshift 1.7, it is a nearly mass-limited sample, an ideal benchmark to test cluster evolution. We developed a pipeline to first separate the cluster signal from the background and foreground components and then jointly fit a parametric profile model on a combination of Planck and SPT data. We validate our algorithm on a subsample of six clusters, common to the SPT and the CHEX-MATE catalogues, comparing the results with the profiles obtained from X-ray observations with XMM-Newton

Cosmology with the SZ spectrum: Measuring the Universe’s temperature with galaxy clusters

The hot gas in clusters of galaxies creates a distinctive spectral distortion in the cosmic microwave background (CMB) via the Sunyaev-Zel’dovich (SZ) effect. The spectral signature of the SZ can be used to measure the CMB temperature at cluster redshift (TCMB(z)) and to constrain the monopole of the y-type spectral distortion of the CMB spectrum. In this work, we start showing the measurements of TCMB(z) for a sample extracted from the Second Catalog of galaxy clusters produced by Planck (PSZ2) and containing 75 clusters selected from CHEX-MATE. Then we show the forecasts for future CMB experiments about the constraints on the monopole of the y-type spectral distortion of the CMB spectrum via the spectrum of the SZ effect

Outcome at three months of COPD patients with acute hypercapnic respiratory failure treated with NPPV in an Acute Medicine Ward

Non invasive positive pressure ventilation (NPPV) is increasingly used for patients with hypercapnic respiratory failure secondary to acute exacerbation of chronic obstructive pulmonary disease (COPD). NPPV has been shown to improve arterial blood gas tensions and dyspnoea and to prevent the need for intubation in patients admitted to hospital with an exacerbation of COPD associated with respiratory acidosis. Although advantages of NPPV over conventional treatment have been convincingly documented in the short period, there are fewer data as to the outcomes following hospital discharge. We have undertaken a prospective descriptive study to obtain comprehensive data on the in hospital and 3 month outcomes of a cohort of 57 COPD patients treated with NPPV for acute hypercapnic respiratory failure as a first intervention in addition to usual medical care. Patients with a COPD exacerbation had better outcomes than patients with COPD complicated by other acute conditions. Pneumonia was specifically associated with a higher inhospital risk of death. In our series about one in four patients with an indicator of previous severe respiratory disease (past admission for acute respiratory failure, previous use of NPPV, long term oxygen therapy or home NPPV) was dead at three months after discharge and almost one in two was dead or had been readmitted. On the contrary, patients without indicators of previous severe respiratory disease benefited from NPPV during an acute episode of respiratory failure and had a chance of approximately 80% of being alive and free from recurrence at three months

CHEX-MATE: pressure profiles of 6 galaxy clusters as seen by SPT and Planck

Pressure profiles are sensitive probes of the thermodynamic conditions and the internal structure of galaxy clusters. The intra-cluster gas resides in hydrostatic equilibrium within the Dark Matter gravitational potential. However, this equilibrium may be perturbed, e.g. as a consequence of thermal energy losses, feedback and non-thermal pressure supports. Accurate measures of the gas pressure over the cosmic times are crucial to constrain the cluster evolution as well as the contribution of astrophysical processes. In this work we presented a novel algorithm to derive the pressure profiles of galaxy clusters from the Sunyaev-Zeldovich (SZ) signal measured on a combination of Planck and South Pole Telescope (SPT) observations. The synergy of the two instruments made it possible to track the profiles on a wide range of spatial scales. We exploited the sensitivity to the larger scales of the Planck High-Frequency Instrument to observe the faint peripheries, and the higher spatial resolution of SPT to solve the innermost regions. We developed a two-step pipeline to take advantage of the specifications of each instrument. We first performed a component separation on the two data-sets separately to remove the background (CMB) and foreground (galactic emission) contaminants. Then we jointly fitted a parametric pressure profile model on a combination of Planck and SPT data. We validated our technique on a sample of 6 CHEX-MATE clusters detected by SPT. We compare the results of the SZ analysis with profiles derived from X-ray observations with XMM-Newton. We find an excellent agreement between these two independent probes of the gas pressure structure