Physics (Internal)

PROBING DARK ENERGY WITH LARGE-SCALE GALAXY CLUSTERING: FROM INSTRUMENTATION TO SIMULATION

This event is part of the PhD Final Oral Exams.

Examining Committee: Steve Ahlen, Martin Schmaltz, Daniel Eisenstein, Edward Kearns, Alex Sushkov

Abstract:

Mapping the Large-Scale Structure of the universe at the Cosmic Frontier is a promising experimental avenue which will address in the next decade several pressing open questions in cosmology and particle physics, most notably the accelerating cosmic expansion. The observed distribution of galaxies and quasars traces the underlying matter density field and contains a wealth of information from signatures of primordial conditions to the background evolution rate. In this colloquium. I will describe our involvement in the instrumentation and in the analysis of cosmological N-body simulations. The Dark Energy Spectroscopic Instrument (DESI) is a next-generation, Stage IV dark energy experiment under construction that will measure the expansion history of the universe through Baryon Acoustic Oscillations and the growth of structure through Redshift-Space Distortions. With an order of magnitude improvement over previous redshift surveys, DESI will place tight constraints on the dark energy equation of state, modified gravity, the existence of extra light species, neutrino masses, and models of inflation. ProtoDESI was the first on-sky demonstration of the critical DESI technology where we successfully acquired targets with fibre positioners and maintained pointing stability. Using coordinate measurement machines, we performed complete metrology on the DESI focal plate structure and aligned 12 production petals to a projected optical throughput of 99.88% ± 0.12% RMS, ensuring minimal loss of photons at the focal surface. Finally, we quantify the shifts of the acoustic scale potentially resulting from galaxy clustering bias, which constitutes an increasingly significant source of theoretical systematics in distance measurements with the standard ruler. Utilising mock catalogues based on generalised halo occupation population of high-accuracy Abacus simulations in the largest volume to date for such tests, 48 h⁻³Gpc³, we find a 0.3% shift in the line-of-sight acoustic scale for one variation in the satellite galaxy population and a 0.7% shift for an extreme level of velocity bias of the central galaxies, while other models tested are consistent with zero shift at the 0.2% level after reconstruction. We note that these bias models produce sizeable and likely distinguishable changes at small scales that correlate with the shifts.