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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)

Three issues were investigated; first, the influence of virus on pigment production in diseased plants; second, the increase of virus as indicated by a resulting change in carotene concentration; third, the function of pigments other than chlorophyll in photosynthesis in young potato leaves. Results on the first issue demonstrated an increase in carotene and xanthophyll concentration, and a decrease in chlorophyll concentration in diseased relative to normal plants. Evidence on the second issue suggested a close relationship between virus increase and carotene concentration. Data on the third issue indicated a soil and possibly significant photosynthesis due to leaf carotenoids / Thesis / Master of Science (MS)

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.