Dissertations, Theses, and Capstone Projects
Date of Degree
6-2026
Document Type
Master's Thesis
Degree Name
Master of Science
Program
Astrophysics
Advisor
Timothy Paglione
Subject Categories
Astrophysics and Astronomy | Physics
Keywords
Galaxy cluster, Gamma-rays, Cosmic rays, high energy, Fermi
Abstract
Galaxy clusters are the largest bound structures in the universe and host many energetic processes. Some of this activity, such as large-scale turbulence and feed- back from starburst superwinds and AGN jets, can cause shocks that accelerate charged particles to relativistic speeds. These cosmic rays interact with the intraclus- ter medium and radiation, producing gamma-rays through proton-proton collisions and inverse Compton scattering. However, barring one or two potential exceptions, galaxy clusters have yet to be confirmed as gamma-ray sources. In this work, we use 16 years of data collected by the Large Area Telescope aboard the Fermi Gamma- Ray Space Telescope to characterize the gamma-ray emission of a population of galaxy clusters selected from the Planck Sunyaev-Zeldovich catalog. We perform binned maximum-likelihood analysis to determine the detection significance of each target. We detect 4 Galaxy Clusters from their gamma ray emissions. The noise- dominated nature of these observations reduces the probability of detecting most clusters individually. We therefore employ a likelihood stacking technique to un- cover the cumulative gamma-ray signal from the subthreshold population. We find that the target galaxy cluster stack considerably exceeds the cumulative likelihood of our two large control field samples, with a significance of over 6σ. The resultant discernible signal confirms the existence of gamma-ray emission from the popula- tion. Further, spectral energy distributions of the sub-threshold population were created and stacked, finding an average spectral index of γ = 2.727 for galaxy cluster gamma-ray emissions. An alternative extended spatial model was investigated and found to be unreliable for this type of emission. We apply several creative methods to discriminate against point-source contaminants (e.g., AGN), including extension fitting, high-redshift control-field comparisons, and test-statistic maps. Likelihood- based correlation analyses with complementary X-ray data reveal no correlations with luminosity, cluster mass, or electron pressure.
Recommended Citation
Eysselinck, Thyra J., "Characterizing Galaxy Cluster Gamma-Ray Emission" (2026). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/6800
