In this PhD Thesis I present my work and its results on the polarized emission from our Galaxy. I studied in particular the dust and synchrotron emissions that contaminate the observations of the Cosmic Microwave Background Radiation (CMB). To separate these foregrounds from the photons of primordial origin is one of the main challenges for achieving the promise of the next generation of CMB polarization experiments. As a member of international Galactic Science Working Groups, I worked in close collaboration with the world-leading current and next-generation telescopes: the Simons Observatory (SO), the Atacama Cosmology Telescope (ACT), and the BLAST (Balloon-borne Large Aperture Submillimeter Telescope) experiment. I am the recognized leader of the power spectrum analysis of multi-frequency Galactic emission published in the collaboration paper Hensley et. al (2022), where I forecasted the ability of SO to improve the constraints of synchrotron and dust spectral parameters in the harmonic domain. I made a fitting of the SED models, using an MCMC method, to simulated auto- and cross-angular power spectra at different frequency channels and angular scales, including the relative noise figures, for E- and B-modes separately, starting from map-level simulations. I set up the work using a set of frequencies from various experiments, i.e. S-PASS, C-BASS, WMAP and Planck, with channels from 2.3 up to 353 GHz, and quantifying the effect of the addition of SO data to existing measurements, finding that the constraints on all the parameters improves by a factor two. I defined the optimal observational strategy for the BLAST-TNG experiment (launched from Antarctica in 2020) and the proposed BLAST Observatory, its successor, identifying the interstellar medium (ISM) fields to be observed with high priority, with the aim of studying the diffuse dust emission for the CMB foreground characterization. I developed and implemented an algorithm to look for some sky patches with features similar to the ones of diffuse, low-intensity and highly-polarized dust regions. I took into account different possible launch dates and the instrument sensitivity and resolution, trying a range of patch sizes and required observational time to find the optimal combination. I developed a selection criterion based on three parameters called "Quality Factors", which are scalar values defined as the average values of the Polarization Fraction, the signal-to-noise ratio (SNR) of the Polarization Fraction, and the SNR of the Polarization Power Contrast of all the pixels within a certain patch. I also analyzed the data from the attitude control system of the BLAST-TNG telescope, which is based mainly on star cameras as sensors to determine the telescope pointing. After a post-flight analysis of about 5,000 stellar images, I managed to increase the number of original post-flight pointing solutions by a factor larger than 4, recovering 1,650 astrometric solutions thanks to the development of advanced filtering techniques to clean all the Polar Mesospheric Clouds that contaminated the images. Finally, I performed a novel analysis to extend existing results on the correlation between the 353 GHz Planck channel and the data from the starlight polarization, up to smaller frequencies. By using existing stellar catalogues, I prepared a star sample based on the same criteria used in the Planck's analysis. I replicated the measurement of the polarization-to-extinction ratio at 217 and 143 GHz, as predicted by dust models at lower frequencies, using the photometric aperture method for the emission data treatment. This analysis is part of a project that plans to exploit the high resolution and sensitivity of ACT data to study this phenomenon by solving small scales. I will publish these results as first author in a paper in preparation.
In questa Tesi di Dottorato presento il mio lavoro e i relativi risultati riguardo l'emissione polarizzata dalla nostra Galassia, sincrotrone e polvere cosmica, che contaminano le osservazioni della radiazione cosmica di fondo (CMB). I progetti che presento sono stati svolti in collaborazione con dei gruppi di lavoro internazionali di scienza galattica, con lo scopo di caratterizzare questi primi piani per poterli poi separare dai fotoni di origine primordiale, nel contesto di alcuni esperimenti di prossima generazione che si occupano di CMB: il Simons Observatory (SO), l'Atacama Cosmology Telescope (ACT) e l'esperimento da pallone stratosferico BLAST (Balloon-borne Large Aperture Sub-millimeter Telescope). Sono il leader riconosciuto dell'analisi dell'emissione galattica multi-frequenza effettuata a livello dello spettro di potenza, e pubblicata nell'articolo della collaborazione Simons Observatoty Hensley et. al (2022), che ha fornito una previsione sulla capacità dell'esperimento SO di migliorare i vincoli esistenti sui parametri spettrali, sia dell'emissione di sincrotrone che di quella della polvere, per la modalità B in polarizzazione. Ho impostato il lavoro utilizzando una serie di frequenze di vari esperimenti, S-PASS, C-BASS, WMAP e Planck, con canali da 2,3 fino a 353 GHz e, a partire da mappe simulate dell'emissione galattica, tramite il calcolo di tutti gli spettri di potenza ottenuti considerando i diversi canali in frequenza, includendo gli spettri di potenza del rumore. Ho infine eseguito un MCMC fitting dei modelli di SED sia del sincrotrone che della polvere, considerando tutte le scale angolari osservabili dall'esperimento. Sono pertanto riuscita a quantificare l'effetto dell'aggiunta che i dati SO apporteranno alle misurazioni esistenti, trovando un miglioramento sui vincoli dei parametri spettrali di circa un fattore due. Ho definito la strategia osservativa per l'esperimento BLAST-TNG (lanciato dall'Antartide nel 2020) e per il proposto BLAST Observatory, suo successore, per quanto concerne lo scopo di studiare l'emissione diffusa della polvere. Ho quindi identificato alcuni campi del mezzo interstellare tramite lo sviluppo sia di un algoritmo che cerca regioni di cielo di polvere diffusa, a bassa intensità e altamente polarizzate, considerando la sensibilità e la risoluzione dello strumento, diverse possibili date di lancio, e la combinazione ottimale tra varie dimensioni dei campi e vari tempi di osservazione, sia di uno specifico criterio di selezione basato su dei parametri che ho chiamato "Fattori di qualità". Ho inoltre analizzato i dati del sistema di controllo dell'assetto del telescopio BLAST-TNG, che si basa principalmente su telecamere stellari come sensori per determinare il puntamento del telescopio. Dopo un'analisi post-volo di circa 5.000 immagini stellari, sono riuscita ad aumentare il numero di soluzioni originali di un fattore superiore a 4, recuperando 1.650 soluzioni astrometriche grazie allo sviluppo di avanzate tecniche di filtraggio per ripulire le immagini dalle nubi mesosferiche polari contaminanti. Infine, ho eseguito una nuova analisi estendendo fino a frequenze minori i risultati esistenti sulla correlazione tra il canale a 353 GHz di Planck e i dati della polarizzazione della luce stellare. Ho replicato la misurazione del rapporto di polarizzazione emissione-estinzione a 217 e 143 GHz, utilizzando la nuova release di dati Planck, ottenendo misure compatibili con quelle previste dai modelli di polvere, e implementando un diverso approccio per il trattamento dei dati di emissione, definito ad apertura circolare fotometrica. Tale analisi è inserita all'interno di un progetto che prevede di sfruttare la maggiore risoluzione e sensibilità dei dati dell'esperimento ACT per ispezionare scale angolari più piccole. Questi risultati saranno pubblicati in un articolo ora in preparazione di cui sono prima autrice.
The polarized emission from our Galaxy: forecasts, measurements, analysis, and characterization as a foreground in the context of current and next-generation Cosmic Microwave Background experiments
FANFANI, VALENTINA
2023
Abstract
In this PhD Thesis I present my work and its results on the polarized emission from our Galaxy. I studied in particular the dust and synchrotron emissions that contaminate the observations of the Cosmic Microwave Background Radiation (CMB). To separate these foregrounds from the photons of primordial origin is one of the main challenges for achieving the promise of the next generation of CMB polarization experiments. As a member of international Galactic Science Working Groups, I worked in close collaboration with the world-leading current and next-generation telescopes: the Simons Observatory (SO), the Atacama Cosmology Telescope (ACT), and the BLAST (Balloon-borne Large Aperture Submillimeter Telescope) experiment. I am the recognized leader of the power spectrum analysis of multi-frequency Galactic emission published in the collaboration paper Hensley et. al (2022), where I forecasted the ability of SO to improve the constraints of synchrotron and dust spectral parameters in the harmonic domain. I made a fitting of the SED models, using an MCMC method, to simulated auto- and cross-angular power spectra at different frequency channels and angular scales, including the relative noise figures, for E- and B-modes separately, starting from map-level simulations. I set up the work using a set of frequencies from various experiments, i.e. S-PASS, C-BASS, WMAP and Planck, with channels from 2.3 up to 353 GHz, and quantifying the effect of the addition of SO data to existing measurements, finding that the constraints on all the parameters improves by a factor two. I defined the optimal observational strategy for the BLAST-TNG experiment (launched from Antarctica in 2020) and the proposed BLAST Observatory, its successor, identifying the interstellar medium (ISM) fields to be observed with high priority, with the aim of studying the diffuse dust emission for the CMB foreground characterization. I developed and implemented an algorithm to look for some sky patches with features similar to the ones of diffuse, low-intensity and highly-polarized dust regions. I took into account different possible launch dates and the instrument sensitivity and resolution, trying a range of patch sizes and required observational time to find the optimal combination. I developed a selection criterion based on three parameters called "Quality Factors", which are scalar values defined as the average values of the Polarization Fraction, the signal-to-noise ratio (SNR) of the Polarization Fraction, and the SNR of the Polarization Power Contrast of all the pixels within a certain patch. I also analyzed the data from the attitude control system of the BLAST-TNG telescope, which is based mainly on star cameras as sensors to determine the telescope pointing. After a post-flight analysis of about 5,000 stellar images, I managed to increase the number of original post-flight pointing solutions by a factor larger than 4, recovering 1,650 astrometric solutions thanks to the development of advanced filtering techniques to clean all the Polar Mesospheric Clouds that contaminated the images. Finally, I performed a novel analysis to extend existing results on the correlation between the 353 GHz Planck channel and the data from the starlight polarization, up to smaller frequencies. By using existing stellar catalogues, I prepared a star sample based on the same criteria used in the Planck's analysis. I replicated the measurement of the polarization-to-extinction ratio at 217 and 143 GHz, as predicted by dust models at lower frequencies, using the photometric aperture method for the emission data treatment. This analysis is part of a project that plans to exploit the high resolution and sensitivity of ACT data to study this phenomenon by solving small scales. I will publish these results as first author in a paper in preparation.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14242/171627
URN:NBN:IT:UNIMIB-171627