Toward Reionization: Experimental Techniques for Space-Based Observation of the Cosmic Infrared Background

Author: Heaton, Grigory James

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Bock, James J.

Committee Members: Zmuidzinas, Jonas; Chang, Tzu-Ching; Padin, Stephen; Bock, James J.

Option: Physics

Abstract

The extragalactic Cosmic Infrared Background (CIB) represents a window into the study of the Epoch of Reionization, an era in the early history of the universe at the end of the Cosmic Dark Ages during which the first stars and galaxies formed. In particular, CIB anisotropy measurements of angular fluctuations as opposed to direct intensity measurements promise to mitigate local foregrounds and reveal insights into the process and timeline of Reionization. Reionization is expected to leave an imprint at characteristic $\theta\gtrsim 1'$ angular scales on the sky within the near-infrared CIB which has not yet been detected. However, several independent experiments including CIBER and Spitzer have detected a statistically significant angular power excess at these scales, with an amplitude suggesting Reionization is not the sole contributor. While the most popular explanation at present is that this excess is produced by stars tidally stripped from their parent galaxies at relatively low redshift (intrahalo light), the exact source of the excess and its properties remain hidden. New experiments developed to study the near-infrared CIB from space where airglow contamination becomes minimal, most prominently SPHEREx, have the potential to reveal the source of this mystery and to identify the contribution from Reionization itself.

This dissertation discusses various experimental and observational techniques related to the study of the CIB and a future measurement of its Reionization component as applied to the SPHEREx all-sky survey and the CIBER-2 sounding rocket experiment. In Chapter 2 (originally published separately), I present novel noise-reduction techniques targeted at improving specifically the large-angular-scale sensitivity of the SPHEREx detectors to optimize study of the CIB at large arcminute-to-degree scales and reduce the impact of $1/f$ noise. In Chapter 3 I discuss the CIBER-2 sounding rocket experiment, a purpose-built instrument for studying the CIB, with a particular focus on upgrades and characterization for the 2nd and 3rd flights; a new design of the cryogenic focal plane array used to support the long-wavelength H2RG detector and a description of its assembly is presented. We apply large-scale noise reduction techniques pioneered on SPHEREx to significantly improve CIBER-2 sensitivity to CIB fluctuations, and developed new applications of these methods for reducing excess $1/f$ or crosstalk noise post-flight. In Chapter 4, I discuss analysis techniques for simulating and removing systematic error produced by depth variations on galaxy surveys applied to the emerging field of CIB redshift tomography. Finally, in Chapter 5, I present preliminary spectra of the far-infrared-correlated Diffuse Galactic Light, a relevant local foreground for extragalactic CIB observations, at near-infrared wavelengths using recent SPHEREx observations, which hint at variation across widely separated regions of the sky.