Estimating the Ultimate Sensitivity of Dwarf Galaxies to the Indirect Detection of Dark Matter

For decades, astronomers and physicists have understood that there exists a new type of matter, unlike that which we see around us. This 'dark matter' does not seem to interact appreciably with light and thus far has only been detected through its gravitational interactions. The nature of this dark matter remains one of the most intriguing, unsolved problems in modern physics. A variety of experiments around the world and in space have attempted to observe dark matter and its interactions for many years. One experimental strategy is referred to as 'indirect detection,' whereby observers use telescopes to search through space for regions with an unexpectedly high number of particles that might be caused by dark matter particles annihilating with each other (or decaying) throughout the cosmos. One such telescope is the NASA and DOE sponsored Fermi Gamma-Ray Space Telescope that orbits the earth about every 90 minutes and scans the entire sky for high energy photons called gamma-rays.

This project has the potential to have a direct impact on the viewpoint held by the scientific community regarding the effect of the upcoming, DOE funded Legacy Survey of Space and Time (LSST) telescope on the indirect search for dark matter. Many scientists within the community have the strong expectation that LSST will discover many 'dwarf galaxies' that are much smaller than our own Milky Way galaxy but are orbiting the Milky Way as they are trapped by its gravitational pull. These new dwarf galaxies are anticipated to lead to a significant increase in the Fermi telescope's ability to discover or constrain the properties of dark matter. This work will provide quantitative estimates for exactly how significant that increase is likely to be, thus making those expectations much more robust. In addition, we will provide a first estimate of the ultimate sensitivity that will be accessible for the indirect detection of dark matter using dwarf galaxies as targets. This aspect of the work is inspired by a well-studied, similar statistical limit created at the point in the future when neutrinos will provide an irreducible background referred to as the 'neutrino floor/fog' for experiments that search for a direct interaction between a dark matter particle and the detector (direct detection experiments).

Key Objectives

• Estimate the prospects for detecting or constraining the annihilation properties of dark matter from new dwarf galaxies that are likely to be detected by LSST.
• Produce a publicly available analysis code able to estimate the ultimate sensitivity of dwarf galaxies to the indirect detection of dark matter based on statistical limitations of the gamma-ray background.

This work will also make a key contribution to the investigation of an excess of gamma-rays coming from the galactic center, first identified in 2009 that might be due to the annihilation of dark matter. Since that time, several groups of researchers have confirmed the presence of the excess, including the Fermi Collaboration itself. This galactic center excess remains one of the most intensely researched subjects in dark matter indirect detection as well as gamma-ray physics in general. The work of this proposal intends to provide a definitive answer as to whether the ultimate sensitivity of the Milky Way dwarf galaxies will be sufficient to confirm or refute the dark matter interpretation of the galactic center excess.