Unveiling the expansion history of the universe with cosmic chronometers and gravitational waves

Borghi, Nicola (2024) Unveiling the expansion history of the universe with cosmic chronometers and gravitational waves, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Astrofisica, 36 Ciclo. DOI 10.48676/unibo/amsdottorato/11090.
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This Thesis explores two novel and independent cosmological probes, Cosmic Chronometers (CCs) and Gravitational Waves (GWs), to measure the expansion history of the Universe. CCs provide direct and cosmology-independent measurements of the Hubble parameter H(z) up to z∼2. In parallel, GWs provide a direct measurement of the luminosity distance without requiring additional calibration, thus yielding a direct measurement of the Hubble constant H0=H(z=0). This Thesis extends the methodologies of both of these probes to maximize their scientific yield. This is achieved by accounting for the interplay of cosmological and astrophysical parameters to derive them jointly, study possible degeneracies, and eventually minimize potential systematic effects. As a legacy value, this work also provides interesting insights into galaxy evolution and compact binary population properties. The first part presents a detailed study of intermediate-redshift passive galaxies as CCs, with a focus on the selection process and the study of their stellar population properties using specific spectral features. From their differential aging, we derive a new measurement of the Hubble parameter H(z) and thoroughly assess potential systematics. In the second part, we develop a novel methodology and pipeline to obtain joint cosmological and astrophysical population constraints using GWs in combination with galaxy catalogs. This is applied to GW170817 to obtain a measurement of H0. We then perform realistic forecasts to predict joint cosmological and astrophysical constraints from black hole binary mergers for upcoming gravitational wave observatories and galaxy surveys. Using these two probes we provide an independent reconstruction of H(z) with direct measurements of H0 from GWs and H(z) up to z∼2 from CCs and demonstrate that they can be powerful independent probes to unveil the expansion history of the Universe.

Tipologia del documento
Tesi di dottorato
Borghi, Nicola
Dottorato di ricerca
Settore disciplinare
Settore concorsuale
Parole chiave
observational cosmology, expansion history, gravitational waves, cosmic chronometers, galaxy evolution, Hubble constant
Data di discussione
9 Aprile 2024

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