Probing the Hubble constant: time delay cosmography of SDSS J1433 with the Hubble Space Telescope and the 2.1-meter Wendelstein telescope

Queirolo, Giacomo (2024): Probing the Hubble constant: time delay cosmography of SDSS J1433 with the Hubble Space Telescope and the 2.1-meter Wendelstein telescope. Dissertation, LMU München: Fakultät für Physik

Abstract

While LCDM cosmology is the most successful cosmological model at our disposal today, being able to explain most of the observed phenomena, it has been challenged by more and more tensions. One of the greatest, both in terms of numerical tension and of the importance of the parameter measured, is the infamous Hubble tension. This refers to the disagreement between measurements of the Hubble constant, which describes the rate of expansion of the Universe, a cornerstone of our cosmological understanding. In recent years the methods for measuring H0 have grown in number and sophistication, and yet, as the uncertainties of the measurements have decreased, the tension has not been solved; in fact, it has increased. Such methods can be roughly divided between "early" and "late" probes of H0, approximately referring to the time of origin of the phenomenon observed. While "early" probes, based for example on the cosmic microwave background, are strongly dependent on the assumed cosmology, "late" probes are generally model-independent but are more susceptible to systematic errors in the measurements. In this context, the time delay cosmographic method is a "late" time probe which can measure H0 directly, without requiring any calibration. This analysis is based on the well-tested general relativity phenomenon of strong gravitational lensing. Given a background variable source and a foreground strong gravitational lens, the time delay between the multiple lensed images can be measured by monitoring and analysing their luminosity over time. A separate modelling analysis of the system can then constrain the mass profile of the lens. The two combined information can then be used to constrain the Hubble constant. In this work, I implemented this analysis based on Hubble Space Telescope archival data and a dedicated observational campaign from the 2.1-meter telescope at Wendelstein. I employed the space-based data by taking advantage of the multiple filters available and their higher resolution to model the lens mass, obtaining a result with 3% precision on the Fermat potential. I instead used the data from the Wendelstein observational campaign to produce the lightcurves of the image and analyse them in order to constrain the time delay, which was obtained with a precision ranging from 8% to 15% depending on the image pair. I then combined the results following a Bayesian approach, reaching a constraint on H0 of 71.3+5.0 -4.5 km/(s*Mpc) with a precision ~6.7% considering random uncertainty. Notably, this work has been mostly independent of major collaborations, such as TDCOSMO, thus providing an unbiased validation of the methodology. Furthermore, the result is proof of the capabilities of the Wendelstein observatory, which should be considered a reliable asset for time delay cosmography or similar projects that require high-sampling, high-quality data.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Cosmology, Gravitational lensing, Galaxies
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 20. September 2024
• 1. Bericht­erstatter:in: Bender, Ralf