Dusty circumnuclear disks (CNDs) in luminous early-type galaxies (ETGs) show regular, dynamically cold molecular gas kinematics. For a growing number of these ETGs, Atacama Large Millimeter/sub-millimeter Array (ALMA) CO imaging and detailed gas-dynamical modeling have yielded moderate to high precision black hole (BH) mass (M_BH) determinations. To date, however, few studies have explored the effects of dust attenuation, or uncertainties in dust corrections, on recovered stellar luminosity models from high angular resolution optical/near-IR observations and M_BH measurements. Recent kinematic studies that modeled ALMA CO data sets have found that uncertainties in the intrinsic central stellar surface brightness slope due to dust may even dominate the BH mass error budgets. From the ALMA archive, we identified a subset of 26 ETGs with clean CO kinematics and good prospects for eventual MBH determination but that did not have sufficiently high angular resolution observations in the optical and near-IR. We have obtained new optical and near-IR Hubble Space Telescope (HST) images of this sample to supplement the archival HST data. Together, these new and archival HST data will enable the mitigation of dusty CND obscuration in the construction of dust-corrected stellar luminosity models, leading to both BH mass measurement and complete error analysis using existing ALMA CO imaging. Here, we present the sample properties, data analysis techniques, and dust-masked stellar surface brightness profiles and luminosity models using the multi-Gaussian expansion formalism. With estimated M_BH/M_⊙ ≳ 10^8 to few x10^9 , securing quality M_BH determinations for this sample of ETGs will significantly improve the high-mass end of the current BH census, facilitating new scrutiny of local BH mass-host galaxy scaling relationships.

The GLIMPSE (Galactic Legacy Mid-Plane Survey Extraordinaire) Point Source Catalog of ~ 30 million mid-infrared sources towards the inner Galaxy, 10 < |l| < 65 degrees and |b| < 1 degree, was used to determine the distribution of stars in Galactic longitude, latitude, and apparent magnitude. The counts versus longitude can be approximated by the modified Bessel function N=N_0*(l/l_0)*K_1(l/l_0), where l_0 is insensitive to limiting magnitude, band choice, and side of Galactic center: l_0= 17-30 degrees with a best fit value in the the 4.5 micron band of l_0=24 +/- 4 degrees. Modeling the source distribution as an exponential disk yields a radial scale length of H= 3.9 +/- 0.6 kpc. There is a pronounced north-south asymmetry in source counts for |l| < 30 degrees, with ~ 25% more stars in the north. For l=10-30 degrees, there is a strong enhancement of stars of m= 11.5-13.5 mag. A linear bar passing through the Galactic center with half-length R_bar=4.4 +/- 0.5 kpc, tilted by phi=44 +/- 10 degrees to the Sun-Galactic Center line, provides the simplest interpretation of this data. We examine the possibility that enhanced source counts at l=26-28 degrees, 31.5-34 degrees, and 306-309 degrees are related to Galactic spiral structure. Total source counts are depressed in regions where the counts of red objects (m_K-m_[8.0] >3) peak. In these areas, the counts are reduced by extinction due to molecular gas and/or high diffuse backgrounds associated with star formation.

Aiming at understanding the role of stellar feedback in galaxy evolution, I present a study of the hot interstellar medium in several representative galaxies, based primarily on X-ray observations as well as theoretical modelling. I find that, in the massive disk galaxies NGC2613 and M104, the observed amount of hot gas is much less than that predicted by current galaxy formation models. Such a discrepancy suggests a lack of appropriate treatments of stellar/AGN feedback in these models. I also find that stellar feedback, primarily in the form of mass loss from evolved stars and energy released from supernovae, and presumably consumed by the hot gas, is largely absent from the inner regions of M104, a galaxy of a substantial content of evolved stars but little current star formation. A natural understanding of this phenomenon is that the hot gas is in the form of a galactic-scale outflow, by which the bulk of the stellar feedback is transported to the outer regions and perhaps into the intergalactic space. A comparison between the observed sub-galactic gas structures and model predictions indicate that this outflow is probably subsonic rather than being a classical supersonic galactic wind. Such outflows are likely prevalent in most early-type galaxies of intermediate masses in the present-day universe and thus play a crucial role in the evolution of such galaxies. For the first time I identify the presence of diffuse hot gas in and around the bulge of the Andromeda Galaxy (M31), our well-known neighbor. Both the morphology and energetics of the hot gas suggest that it is also in the form of a large-scale outflow. Assisted with multiwavelength observations toward the circumnuclear regions of M31, I further reveal the relation between the hot gas and other cooler phases of the interstellar medium. I suggest that thermal evaporation, mostly likely energized by Type Ia supernovae, acts to continuously turn cold gas into hot, a process that naturally leads to the inactivity of the central supermassive blackhole as well as the launch of the hot gas outflow. Such a mechanism plays an important role in regulating the multi-phase interstellar medium in the circumnuclear environment and transporting stellar feedback to the outer galactic regions.

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<p>The gravitational collapse of a giant molecular cloud produces localized dense regions, called clumps, within which low-mass star formation is believed to occur. Recent studies have shown that limitations of current observing techniques make it difficult to correctly identify and measure properties of these clumps that reflect the true nature of the star-forming regions. In order to make a direct comparison with observations, we produced synthetic column density maps and a spectral-line cube from the simulated collapse of a large 5000 solar mass molecular cloud. The synthetic observations provide us with the means to study the formation of star-forming clumps and cores in our simulation using methods typically used by observers. Since we also have the full 3D simulation, we are able to provide a direct comparison of `observed' and `real' star-forming objects, highlighting any discrepancies in their physical properties, including the fraction of cores which are gravitationally bound. We have accomplished this by studying the global properties of the star-forming objects, in addition to performing a direct correlation of individual objects to determine the error in the observed mass estimates. By correlating the clumps found in the simulation to those found in the synthetic observations, we find that the properties of objects derived from the spectral-line data cube were more representative of the true physical properties of the clumps, due to effects of projection greatly impacting the estimates of clump properties derived from two-dimensional column density maps.</p> / Master of Science (MSc)

<p>A deep, wide-field survey was conducted to hunt for the light echo systems associated with SN 1054 (Crab) and SN 1181 as an initial step to acquiring spectra and the prospect of extracting lightcurves of these historical, core-collapse supernovae. Images were acquired by the Canada-France-Hawaii Telescope’s MegaCam during the 2011A and 2011B semesters for fields adjacent to SN 1054 and SN 1181, respectively. A total of 367 Sloan g’ fields for the Crab and 195 Sloan r’ fields for SN 1181 were imaged twice, with a minimum of one month separation.</p> <p>Examination of 13,880 and 11,052 difference images for the Crab and SN 1181, respectively, revealed no light echoes with surface brightnesses brighter than 24.0 mag/arcsec² (the threshold for being able to acquire useful spectra). Based on our non-detections and assuming similar dust properties to nearby (detected) supernova light echo systems (Tycho and Cas A), we conclude it is unlikely that either SN was a Type II-L outburst but cannot provide constraints on other sub-types.</p> <p>We further examined the known light echo locations for Tycho and Cas A and found a statistically-significant correlation between CO brightness temperature and the presence of scattering dust. However, the spacing of grid points in existing CO surveys is too sparse to be useful even a few degrees away from the galactic plane. We have yet to identify a search strategy based on survey data which is superior than random field placement.</p> / Master of Science (MSc)

<p dir="ltr">In this dissertation, we develop novel methods of performing shear measurements in individual exposures and apply them to images obtained from WIYN-ODI. We generalize forced photometry and call this new method forced measurement. This involves performing a single iteration of a traditional moment-matching algorithm with reasonable initial guess values and correcting for negative pixel values after background subtraction. We find that this allows us to make flux, shape, size, and ellipticity measurements at extremely low S/N < 1. We compare the performance of this method to existing approaches and find our method to be superior. A novel Monte Carlo PSF correction scheme is also introduced that allows us to dramatically increase the source density and hence perform more accurate weak lensing. These methods are then applied to measure shear across 411 ×30 individual exposures of the galaxy cluster Abell 2390. We find that we are successfully able to recover the main mass structures. We also find that we are able to recover the smaller galaxy groups over a very large field. Examining data from a variety of wavelengths and sources such as X-ray, Radio, and spectroscopic methods, we find Abell 2390 is likely to be a case of late-stage merger. The hot gas during the infall phase experienced friction causing loss of angular momentum and hence is almost merged with the main core. The Dark Matter (DM) cores, however, did not experience such friction and continue to be in the merger phase.In this dissertation, we develop novel methods of performing shear measurements in individual exposures and apply them to images obtained from WIYN-ODI. We generalize forced photometry and call this new method forced measurement. This involves performing a single iteration of a traditional moment-matching algorithm with reasonable initial guess values and correcting for negative pixel values after background subtraction. We find that this allows us to make flux, shape, size, and ellipticity measurements at extremely low S/N < 1. We compare the performance of this method to existing approaches and find our method to be superior. A novel Monte Carlo PSF correction scheme is also introduced that allows us to dramatically increase the source density and hence perform more accurate weak lensing. These methods are then applied to measure shear across 411 ×30 individual exposures of the galaxy cluster Abell 2390. We find that we are successfully able to recover the main mass structures. We also find that we are able to recover the smaller galaxy groups over a very large field. Examining data from a variety of wavelengths and sources such as X-ray, Radio, and spectroscopic methods, we find Abell 2390 is likely to be a case of late-stage merger. The hot gas during the infall phase experienced friction causing loss of angular momentum and hence is almost merged with the main core. The Dark Matter (DM) cores, however, did not experience such friction and continue to be in the merger phase.In this dissertation, we develop novel methods of performing shear measurements in individual exposures and apply them to images obtained from WIYN-ODI. We generalize forced photometry and call this new method forced measurement. This involves performing a single iteration of a traditional moment-matching algorithm with reasonable initial guess values and correcting for negative pixel values after background subtraction. We find that this allows us to make flux, shape, size, and ellipticity measurements at extremely low S/N < 1. We compare the performance of this method to existing approaches and find our method to be superior. A novel Monte Carlo PSF correction scheme is also introduced that allows us to dramatically increase the source density and hence perform more accurate weak lensing. These methods are then applied to measure shear across 411 ×30 individual exposures of the galaxy cluster Abell 2390. We find that we are successfully able to recover the main mass structures. We also find that we are able to recover the smaller galaxy groups over a very large field. Examining data from a variety of wavelengths and sources such as X-ray, Radio, and spectroscopic methods, we find Abell 2390 is likely to be a case of late-stage merger. The hot gas during the infall phase experienced friction causing loss of angular momentum and hence is almost merged with the main core. The Dark Matter (DM) cores, however, did not experience such friction and continue to be in the merger phase.</p>