From Lab to Sky: Advancing CMB Research with the Simons Observatory and Atacama Cosmology Telescope

Abstract

In recent decades, observations of the Cosmic Microwave Background (CMB) have solidified our understanding of the standard ΛCDM cosmology model, and enhanced our comprehension of Dark Energy, Dark Matter, and primordial fluctuations. The CMB continues to be a valuable resource for deepening our cosmic knowledge.This thesis provides an overview of the Atacama Cosmology Telescope (ACT), situated at 5190 meters on Cerro Toco in Chile’s Atacama Desert. It discusses the on-sky performance of the ACT detectors, with a particular focus on the detector time constants after the final receiver upgrade. ACT completed its last data collection on July 1st, 2022. Adjacent to ACT, the Simons Observatory (SO) consists of a 6 m large aperture telescope (LAT) and three 0.5 m small aperture telescopes (SATs). At the time of writing, SO has deployed all telescope receivers and has begun scientific operations with two of the SATs. SO employs a novel frequency-domain multiplexing read- out system and is equipped with approximately 68,000 transition-edge sensor (TES) bolometers. SO is poised to deliver precise measurements of CMB temperature and polarization fluctuations across six frequency bands, ranging from 30 to 280 GHz. It offers sensitivity that could be up to ten times greater, angular resolution about five times higher than the Planck satellite, and approximately a tenfold increase in mapping speed compared to current ground-based CMB experiments. This thesis provides an overview of the SO detector and readout, and details the efforts to vali- date and understand the performance of the detector modules. Additionally, it covers the laboratory testing, commissioning, and initial field performance of one SO SAT: TSAT.