UCLA

This thesis presents progress in two subfields of astrophysics, first in galactic astronomy, describing how a large survey of ground-state silicon monoxide emission can probe asymptotic giant branch stellar envelope expansion, and second in observational cosmology, presenting novel constraints on primordial black holes (PBH) as a fraction of dark matter by leveraging strong gravitational lensing. The Galactic project searched the Very Large Array Bulge Asymmetries and Dynamical Evolution (BAaDE) survey for maser and thermal emission from the $J=1-0, v=0$ ground vibrational state transition. I present results characterizing these sources as a nearby disk population and derive the expansion velocity of the emission region by fitting thermal components of lines to an emission model. For the small number of sources with corresponding carbon monoxide emission, I find the expansion velocities to be similar for both the thermal SiO and CO, evidence that both emissions are produced in the same region above the star where the gas has reached terminal velocity. In the cosmology portion of the thesis, the objective is to use a flux-ratio analysis to put constraints on intermediate-mass PBH as a possible fraction of dark matter. A population of PBH within the dark matter halo of a lensing galaxy would affect the magnification, and therefore the flux ratios, of the images in a quadruply-imaged quasar (quad). By forward-modeling the flux ratios using an Approximate Bayesian Computing technique, I obtain a constraint on PBH within the mass range of $10^4 $M$_{\odot}