2025 Theses Doctoral

Cosmology and astrophysics with non-Gaussian signals and spectral distortions

Sabyr, Alina

In this thesis, we examine several cosmological and astrophysical probes: weak gravitational lensing (WL), thermal Sunyaev-Zeldovich effect (tSZ), and spectral distortions. Each of these signals can provide unique ways to test and reveal different components of the standard cosmological model, and to improve our understanding of the small-scale astrophysical processes.

In Chapter 2, we investigate if future analyses, which employ the WL non-Gaussian summary statistic `peak counts,' could use simulations based on dark matter halos alone. We find that such simplified models, compared to full N-body simulations, could lead to biases.

In Chapter 3, we study the cosmological constraining power of five tSZ summary statistics (power spectrum, Minkowski functionals, peaks, minima, and moments). We show that we can extract significant non-Gaussian information from the tSZ signal and, thus, improve the constraints compared to those expected from the power spectrum alone.

In Chapter 4, we study the sensitivity of the tSZ Minkowski functionals to electron pressure.

In Chapter 5, we compute a spectral distortion in the cosmic infrared background (CIB) due to scattering of the CIB photons off of energetic electrons along the line of sight, similar to the sky-averaged tSZ effect in the cosmic microwave background (CMB). This new signal could be detected by future spectral distortion missions.

In Chapter 6, we present a new instrument concept for a space mission to measure the primordial 𝜇-distortion in the CMB. We determine an instrument configuration that is capable of detecting it at high significance even after astrophysical foreground marginalization.

In Chapter 7, we perform a re-analysis of the 𝘊𝘖𝘉𝘌/𝘍𝘐𝘙𝘈𝘚 data and present new constraints on the 𝑦-distortion in the CMB. We carry out a comparison between two analysis approaches and validate the current forecasting methods for spectral distortion experiments.