Millimeter Observations of Molecular Interstellar Medium from Parsec to Kiloparsec Scales

Author: ORCID icon
Bittle, Lauren, Astronomy - Graduate School of Arts and Sciences, University of Virginia
Johnson, Kelsey, As-Astronomy, University of Virginia

Star formation is a fundamental driver of galaxy evolution. Understanding the intricacies of star formation requires a keen understanding of the physical makeup of their natal molecular material. Probing the molecular gas content of the interstellar medium, we aim to better determine the internal physical properties of the molecular structures to thus have a better grasp on the proceeding star formation. We aim to utilize millimeter/submillimeter observations to determine the impact of galaxy environment, both global and local, on the measured and derived physical properties of molecular structures in a range of galaxy types.

Chapter 2 explores the dense molecular clumps within the 30 Doradus region of the Large Magellanic Cloud (LMC), a low metallicity dwarf galaxy only 50~kpc away from Earth. We utilize high resolution (sub-parsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of high critical density gas tracers HCO$^+$, HCN, and CS to track the clumps. The specific molecular cloud 30Dor-10 in which the clumps are contained lies only 15~pc away from the super star cluster R136. We identify molecular clumps in 30Dor-10 then measure (LTE) and model (non-LTE) their internal physical properties. We compare those properties as a function of projected distance away from R136 to assess the impact of the harsh ultraviolet radiation on the clumps.

Observations and analysis of the sole Local Group dwarf starburst, IC~10, are presented in Chapter 3. We use observations from IRAM 30-m and Arizona Radio Observatory Submillimeter Telescope single dish facilities of CO~(1-0), CO~(2-1) and the corresponding $^{13}$CO isotopologues to identify giant molecular clouds (GMCs; $\sim$150~pc) across the main body of the dwarf. We test how gas properties vary in a sub-solar metallicity environment with regions of unique localized conditions (shocks/PDR, infalling cloud). IC 10 is isolated from a massive host, which disentangles the results from a merging situation, such as in the case with the LMC. In addition, we present results from pointed spectroscopy of dense gas (HCO$^+$, HCN) observations from the Green Bank Telescope of molecular clouds in IC~10. We discuss the impact of the large-scale structure of the HI on the dense gas properties.

Chapter 4 discusses the high resolution ALMA CO~(2-1) observations of a nearly face-on flocculent spiral NGC 7793. Utilizing the maximum mosaicking capabilities of ALMA, we map 3~$\times$~2~kpc of the spiral with sub-arcsec resolution. We present the catalog of clouds ($\sim$20~pc) identified across the spiral galaxy in comparison with the stellar clusters identified by the Legacy ExtraGalactic Ultraviolet (UV) Survey (LEGUS) team using the Hubble Space Telescope. We aim to test the impact of large-scale spiral structure on theories of cloud and clusters associations and lifetimes.

PHD (Doctor of Philosophy)
molecular gas, extragalactic star formation, interstellar medium
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