A Systematic Search of Dark Matter Subhalos in Gamma Rays among Unidentified Sources and Constraints on Dark Matter Properties

October 1, 2021
11:00am to 12:30pm

Audiovisual Room and Zoom

Specialist level
Javier Coronado

Audiovisual Room and Zoom


This thesis explores how unidentified gamma-ray sources (unIDs) may be used as targets for indirect dark matter (DM) detection. In the first part of the thesis, we develop a general strategy to search for unIDs compatible with a DM origin with the space-borne Fermi-LAT gamma-ray telescope. By characterizing the instrumental sensitivity to DM and a state-of-the-art N-body cosmological simulation to include unresolved, low-mass DM subhalos, we are able to “filter” the pool of 1500 Fermi-LAT unIDs, leading to just some tens of “VIP” candidates, as well as setting constraints to the DM annihilation cross section. Then, by performing a spectral and spatial analysis, we highlight a few of these VIP candidates as possible DM subhalos, as well as improving our constraints. In the way, we search for stellar streams and develop a new parameter space as input for machine learning classification algorithms to disentangle the pulsar/DM spectral confusion. We find all our candidates as point-like sources, yet we explore the assumption of spatial extension by performing thousands of simulations to study the instrumental performance in the case of extended DM subhalos. We find that, even when considering extreme models, the expected spatial signature is very similar and can be resolved by the Fermi-LAT with the sufficient flux. Finally, we use these results to search for new candidates in the latest source catalogs, finding a handful of unIDs which are remarkably well fitted to DM annihilation.

In the second part of the thesis, we explore alternative experiments and candidates. We use the ground-based HAWC observatory to search for high-latitude unIDs and study their compatibility with a DM origin. Only one source, which turns out to be spatially extended, presents a spectrum compatible with heavy DM annihilation. As HAWC data is not publicly available, we can just set constraints to the cross section, which are very competitive for >1TeV WIMPs. We also explore the future-generation CTA instrument performance. As this is currently under construction, we can rely just on simulated data. We develop three different search strategies and characterize its instrumental threshold sensitivity to DM. By extrapolating MAGIC observations, we are able to predict the observational strategy of CTA in the first 10 years of operation. With this information, we are able to set constraints, which complement the Fermi-LAT and HAWC ones. Finally, we study primordial black holes (PBHs) as an alternative candidate for DM. If DM was at least partly composed by a light PBH population, their evaporation through Hawking radiation would leave an imprint on the high-energy (X-ray and gamma-ray) isotropic cosmological background. By using data from several experiments, as well as state-of-the-art modeling of the AGN population, we are able to set constraints to the fraction of PBHs as a function of their mass, partially ruling out one of the open windows for PBHs.