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Despite valiant effort by astronomers, the mass of the Milky Way (MW) Galaxy is poorly constrained, with estimates varying by a factor of two. A range of techniques have been developed and different types of data have been used to estimate the MW’s mass. One of the most promising and popular techniques is to use the velocity and position information of satellite objects orbiting the Galaxy to infer the gravitational potential, and thus the total mass. Using these satellites, or Galactic tracers, presents a number of challenges: 1) much of the tracer velocity data are incomplete (i.e. only line-of-sight velocities have been measured), 2) our position in the Galaxy complicates how we quantify measurement uncertainties of mass estimates, and 3) the amount of available tracer data at large distances, where the dark matter halo dominates, is small. The latter challenge will improve with current and upcoming observational programs such as Gaia and the Large Synoptic Survey Telescope (LSST), but to properly prepare for these data sets we must overcome the former two. In this thesis work, we have created a hierarchical Bayesian framework to estimate the Galactic mass profile. The method includes incomplete and complete data simultaneously, and incorporates measurement uncertainties through a measurement model. The physical model relies on a distribution function for the tracers that allows the tracer and dark matter to have different spatial density profiles. When the hierarchical Bayesian model is confronted with the kinematic data from satellites, a posterior distribution is acquired and used to infer the mass and mass profile of the Galaxy. This thesis walks through the incremental steps that led to the development of the hierarchical Bayesian method, and presents MW mass estimates when the method is applied to the MW’s globular cluster population. Our best estimate of the MW’s virial mass is 0.87 (0.67, 1.09) x 10^(12) solar masses. We also present preliminary results from a blind test on hydrodynamical, cosmological computer-simulated MW-type galaxies from the McMaster Unbiased Galaxy Simulations. These results suggest our method may be able to reliably recover the virial mass of the Galaxy. / Thesis / Doctor of Philosophy (PhD)

The Fermi Large Area Telescope has observed a gamma-ray excess toward the center of the Galaxy at ~ GeV energies. The spectrum and intensity of the excess are consistent with the annihilation of dark matter with a mass of ~100 GeV and a velocity-averaged cross section of ~ 1e-26 cubic centimeter per second. In the meantime, a population of unresolved millisecond pulsars (MSPs) in the Galactic center remains a possible source of the excess. Furthermore, recent analyses have shown that the excess prefers the spatial morphology of the stellar bulge distribution in the Galactic center, supporting a MSP origin. The new discovery makes it imperative to further study the signals from MSPs. This dissertation studies the gamma-ray emission from Galactic millisecond pulsars to provide new insights into the origin of the Galactic center excess. Using the GALPROP code, we simulate the propagation of e± injected by the putative MSPs in the Galactic bulge and calculate the inverse Compton (IC) emission caused by the e± losing energy in the interstellar radiation field. We find recognizable features in the spatial maps of the IC. Above TeV energies, the IC morphology tends to follow the distribution of the injected e±. Then, we study the Cherenkov Telescope Array (CTA) sensitivity to the IC signal from MSPs. We find that the CTA has the potential to robustly discover the IC signature when the MSP e± injection efficiencies are in the range ≈ 2.9-74.1%. The CTA can also discriminate between an MSP and a dark matter origin for the radiating e± based on their different spatial maps. Next, we analyze the Fermi data from directions of Galactic globular clusters. The globular clusters are thought to be shining in gamma rays because of the MSP population they host. By analyzing their gamma-ray spectra, we reveal evidence for an IC component in the high-energy tail of Fermi data. Based on the IC component in the globular cluster spectra, the e± injection efficiency of millisecond pulsars is estimated to be slightly smaller than 10%. Finally, we study the spatial morphology of the 511 keV signal toward the Galactic center using data from INTEGRAL/SPI. We confirm that the 511 keV signal also traces the old stellar population in the Galactic bulge, which is similar to the Fermi GeV excess. Using a 3D smoothing kernel, we find that the signal is smeared out over a characteristic length scale of 150 ± 50 pc. We show that positron propagation prior to annihilation can explain the overall phenomenology of the 511 keV signal. / Doctor of Philosophy / Dark matter means matter that does not interact with light; therefore, they are invisible to traditional observations. We know that dark matter exists based on plenty of gravitational evidence: the motions of stars in galaxies, the large-scale structure of the Universe, the temperature fluctuations in the cosmic microwave background. However, we still know very little about the particle nature of dark matter. Detecting dark matter is one of the most extensive missions of modern physics. In indirect detection, the dark matter particles are expected to annihilate or decay in the cosmos, producing messenger particles that include gamma rays, cosmic rays, and neutrinos. Astronomical observations could detect those signals and confirm the nature of dark matter. However, understanding the astrophysical sources is essential for indirect detection of dark matter as they may emit similar signals. For a recent example, the Fermi Large Area Telescope launched by NASA is the most sensitive gamma-ray telescope in the energy range of ~ 100 MeV to ~ 100 GeV. It has detected an excess of gamma-ray signals toward the Galactic center consistent with what we expect from dark matter annihilation. However, millisecond pulsars, a type of fast rotating neutron stars, may also generate similar gamma-ray signals. Therefore, the origin of the signal remains unsettled. In this dissertation, we study different prospective of the gamma-ray emission from the millisecond pulsars in the Milky Way. We first study the inverse Compton signal from the millisecond pulsars in the Galactic bulge, caused by the relativistic e± injected by the millisecond pulsars. We find that the signal traces the original distribution of the e± above TeV energies. Next generation ground-based gamma-ray observatories like the Cherenkov Telescope Array (CTA) could be used to detect the signal. We study the CTA sensitivity to such an inverse Compton signal. We find that CTA can detect the inverse Compton signal from millisecond pulsars and discriminate it from a dark matter signal. We also study the gamma-ray emission from globular clusters in the Milky Way. They are dense collections of old stars orbiting our Galaxy, and they are known for hosting many millisecond pulsars. We reveal evidence for inverse Compton emission from the gamma-ray data of globular clusters. Our discovery helps us better understand the high-energy property of millisecond pulsars. Last, we study the morphology of the Galactic 511 keV signal caused by positron annihilation. Compact objects including millisecond pulsars are potential sources of the positrons. We find that the old stellar distribution with a smearing scale of ~ 150 pc best describes the 511 keV signal. Positron propagation from their sources prior to annihilation could explain the measured smearing scale.

The standard model of particle physics cannot currently explain the origin of neutrino masses and anomalies that have been observed at different experiments. One solution for this is to introduce a beyond the standard model origin for these issues, which introduces a coupling between neutrinos and dark matter. Such an interaction would have implications on cosmology and would be constrained by astrophysical neutrino sources. A promising astrophysical source to probe this interaction is core-collapse supernovae as they release ~3x10^53 erg in neutrinos for each transient. However, more observations that constrain the internal physics of core-collapse supernovae are needed in order to better understand their neutrino emission. This dissertation studies two probes of internal physics that allow for a better understanding of the neutrino emission from core-collapse supernovae. The first is a novel approach to try and detect more supernova neutrinos that do not come from galactic events nor from the diffuse supernova background. This is accomplished by doing an offline timing coincidence search at neutrino detectors with a search window determined by optical observations of core-collapse supernovae. With a two-tank Hyper-Kamiokande, this allows for ~1 neutrino detection every 10 years with a confidence level of ~2.6 sigma, resulting from low nearby core-collapse rates and large background rates in the energy range of interest. The second probe of internal physics is high energy gamma-rays from the decays of unstable nuclei in proto-magnetar jets. The abundance distribution of the unstable nuclei depends directly on the neutrino emission, which controls the electron fraction, as well as properties of the proto-magnetar. We find that different proto-magnetar properties produce gamma-ray signals that are distinguishable from each other, and multiple types of observations allow for estimations of the jet and proto-magnetar properties. These gamma-ray signals are detectable for on-axis jets out to extragalactic distances, ~35 Mpc in the best case, and for off-axis jets the signal is only detectable for galactic or local galaxies depending upon the viewing angle. This dissertation also studies a phenomenological constraint on the interactions between neutrinos and dark matter. Using the neutrino emission from supernovae and the inferred dark matter distributions in Milky Way dwarf spheroidals, we constrain the amount of energy the neutrinos can inject into the dark matter sub-halos. This then allows a constraint on the interaction cross-section between neutrinos and dark matter with assumptions about the interaction kinematics. Assuming Lambda-CDM to be correct, the neutrinos cannot interact with low mass dark matter too often as it will become gravitationally unbound, changing the mass of the core we see today. For high mass dark matter, neutrinos can only inject a fraction of ~6.8x10^-6 of their energy in order to not conflict with estimates of the current shapes of the dark matter sub-halos. The constraints we obtain are sigma_nu-DM(E_nu=15 MeV, m_DM>130 GeV) ~ 3.4x10^-23 cm^2 and sigma_nu-DM(E_nu=15 MeV, m_DM <130 GeV) ~ 3.2x10^-27} (m_DM/1 GeV)^2 cm^2, which is slightly stronger than previous bounds for these energies. Consideration of baryonic feedback or host galaxy effects on the dark matter profile can strengthen this constraint. / Doctor of Philosophy / In our current understanding of the physics of the particles that govern how the universe behaves, there is no way to explain the properties we observe for the neutrino. Neutrinos were originally theorized to have zero mass, however neutrino experiments suggests otherwise. The current model of particle physics cannot explain how the neutrinos have mass, therefore an viable way to explain it is to introduce new physics that can generate the neutrino masses. A way to do this is to allow the neutrinos to interact with dark matter, which is matter that does not interact with light and is therefore invisible to the human eye. We know dark matter should exist in the universe due to the gravitational effects it has, making things like galaxies much heavier than what the stars and gas we see can explain. If neutrinos and dark matter interact, we should be able to see the effects of these interactions in the universe, and also possibly at locations where many neutrinos are produced. One such source of neutrinos in the universe are core-collapse supernovae, which are the deaths of massive stars and produce copious amounts of neutrinos. This dissertation studies signals that allow us to better understand the neutrino emission from core-collapse supernovae. One of these signals comes from summing the neutrinos we detect from many distant core-collapse supernovae. This technique uses the optical observations of the supernovae to give us a time window around which we can go through neutrino detector data to find if there are any neutrino detections that cannot be explained as coming from background events. Another method is to observe gamma-rays, high energy photons, that come from the radioactive decay of elements in jets moving near the speed of light powered by rare core-collapse supernovae. The specific gamma-rays and the overall brightness of them allows for an estimation of the properties of the neutrino emission and properties of the central engine that accelerates the jet to near the speed of light. This dissertation also studies the implications of a possible interactions in small and dim satellite galaxies of the Milky Way known as dwarf spheroidals. The shape of the dark matter that is distributed in these dwarf spheroidals can be inferred from the motion of the stars in that dwarf spheroidal, and this shape disagrees with the prevailing theory of dark matter in the universe. We take advantage of this disagreement to place an upper limit on both the mass loss that can occur in this region and the energy that past core-collapse supernovae within the dwarf spheroidals can inject into the dark matter. The mass loss bound lets us place a constraint on how often neutrinos can interact with light dark matter particles. The energy injection limit and an assumption on the energy transfer in each interaction between dark matter and neutrinos allows us to constrain how often the interaction can occur for heavy dark matter particles.

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