| Resum: |
Amb la combinació d'estudis cosmològics d'alt volum i un examen detallat dels errors sistemàtics, la nostra comprensió dels paràmetres que governen el nostre Univers ha augmentat dràsticament durant les últimes tres dècades. A finals del segle XX, les primeres mesures van restringir els paràmetres que descrivien l'estructura a gran escala (LSS) i l'expansió de l'univers fins al nivell del 10%. Actualment, col·laboracions com el Dark Energy Survey han restringit els paràmetres a una precisió percentual, i es preveu que futurs estudis com el Vera Rubin Observatory / LegacySurvey of Space and Time (LSST) i el Zwicky Transient Facility (ZTF) observin prou cel per aconseguir una precisió inferior al percentatge. Per garantir que aquests resultats no estiguin esbiaixats, cal un examen detallat dels errors sistemàtics. En aquesta tesi, contribuïm a la quantificació de les incerteses sistemàtiques associades a les mesures de LSS i l'expansió de l'Univers, amb un enfocament particular en les sondes de lent feble i supernoves de tipus Ia (SN Ia). |
| Resum: |
Gracias a la combinación de estudios cosmológicos de gran volumen y un análisis minucioso de los errores sistemáticos, nuestra comprensión de los parámetros que rigen nuestro Universo ha aumentado drásticamente en las últimas tres décadas. A finales del siglo XX, las primeras mediciones permitieron determinar los parámetros que describen la Estructura a Gran Escala (EGE) y la expansión del universo con una precisión del 10 %. Actualmente, colaboraciones como el Sondeo de Energía Oscura han determinado parámetros con una precisión porcentual, y se prevé que futuros sondeos como el Observatorio Vera Rubin/Sondeo Legado del Espacio y el Tiempo (LSST) y el Zwicky Transient Facility (ZTF) observen una porción suficiente del cielo para alcanzar una precisión inferior al 1%. Para garantizar que estos resultados no estén sesgados, es necesario un análisis detallado de los errores sistemáticos. En esta tesis, contribuimos a la cuantificación de las incertidumbres sistemáticas asociadas a las mediciones de la EGE y la expansión del Universo, con especial atención a las lentes gravitacionales débiles y las supernovas de tipo Ia (SN Ia). |
| Resum: |
With the combination of high-volume cosmological surveys and close examination of systematic errors, our understanding of the parameters that govern our Universe has increased dramatically over the last three decades. In the late twentieth century, early measurements constrained parameters describing Large Scale Structure (LSS) and the expansion of the universe to the 10-percent-level. At present, collaborations such as the Dark Energy Survey have constrained parameters to percent-level precision, with future surveys such as the Vera Rubin Observatory / LegacySurvey of Space and Time (LSST) and the Zwicky Transient Facility (ZTF) projected to observe enough of the sky to achieve sub-percent precision. To ensure that these results are not biased, a close examination of systematic errors is necessary. In this thesis, we contribute to the quantification of systematic uncertainties associated with measurements of LSS and the expansion of the Universe, with a particular focus on weak lensing and Type Ia supernova (SN Ia) probes. In Chapters 3 and 4, we develop tools for better understanding systematic errors in weak lensing analyses. In Chapter 3, we develop a method for quick redshift distribution determination for source galaxies from the Bayesian Fourier Domain (BFD) pipeline, which we call Gamgee. We verify that, at the redshift calibration level, Gamgee is a valid replacement for the computationally expensive Balrog source injection method. We also generate calibrated redshift distributions, which, after further tests, will be ready to be used as inputs to the Dark Energy Year 6 (DESY6) analysis framework. In Chapter 4, we develop a new regime of Galaxy-Galaxy Lensing (GGL) measurements, where the lens (position) galaxy sample has a higher mean redshift than the source (shape) sample. We use LSST year 1 forecasts to model potential constraining power for this Inverse Galaxy-Galaxy Lensing (IGGL) data vector. We show that this analysis setup isolates systematic effects associated with the GGL vector, such as magnification, Intrinsic Alignments (IA), and baryonic effects, while removing reliance on galaxy bias. As a result, when combined with cosmic shear and clustering, IGGL is projected to improve constraints on S8 by over 20%. In Chapters 5 and 6, we outline and improve upon pipelines that are used in SN Ia cosmology pipelines. In Chapter 5, we rebuild, and improve upon, a density-velocity pipeline that constrains f σ8 alongside other cosmological parameters, called Theseus. We analyze a low-redshift cut of the Pantheon+ and Union3 datasets in this pipeline, altering analysis choices from both SN Ia compilations to understand how treatments of systematic errors affect constraints of f σ8. We find that fixing Ωm, as is done in previous measurements of f σ8 with SN Ia, can result in artificially low f σ8 errors, which might be the cause of current discrepancies in density-velocity measurement approaches. We further find that posteriors on our low-redshift sample color-dependent nuisance parameters disagree with the full-sample expectations from Pantheon+ and Union3. We find that this is consistent with very recent findings, where consistency checks find low-redshift SN Ia are not treated properly in the Pantheon+ and Union3 datasets. In Chapter 6, we discuss a pipeline for the reduction of SN Ia spectra in the Near-Infrared (NIR), which has been used to examine multiple SNe, both type Ia and otherwise. |
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