Physics & Astronomy ETDs

Publication Date

Fall 9-14-2017

Abstract

The energy and momentum injected into the ISM from stars has a drastic effect on the star formation history of a galaxy. This is called feedback. It is responsible for the inefficient collapse of the ISM into stars. The ``Survey of Water and Ammonia in Nearby Galaxies" (SWAN) is a survey of molecular line tracers in four nearby galaxies. By using molecular tracers of feedback, we provide insights into the star forming ecosystem of the galaxies NGC 253, IC 342, NGC 6946, and NGC 2146. These galaxies were chosen to span an order of magnitude in star formation rate and a variety of galaxy ecosystems. We have selected the metastable NH3 lines as a temperature tracer of the dense molecular ISM, the 22 GHz H2O (616-523) maser as an indicator of star formation, and the 36 GHz CH3OH (4-14-303) maser which was previously unexplored in the extragalactic context. Observations of these galaxies with the Very Large Array (VLA) provides access to 0.1 to 100 pc scales where we can observe how feedback affects the ISM. We uncover evidence for a uniform two-temperature component distribution of the molecular gas across the central kiloparsec of NGC 253 and IC 342. The temperature distribution does not correlate with any observed feedback effects suggesting that no single effect (supernovae, stellar winds, PDRs, or shocks) dominates. We identify several new water masers associated with star formation across all four galaxies. We also show that extragalactic 36 GHz CH3OH masers are 10's of times more luminous as their Milky Way counterparts, and they are likely related to large scale weak shocks in the dense molecular ISM. The luminosity of both the H2O and CH3OH masers appears to correlate with the local star formation rate. In NGC 253 specifically, we test models of galactic outflows driven by a nuclear starburst with sub-arcsecond observations of NH3(3,3) masers, H2O masers and CH3OH masers. From locations and kinematics of the H2O masers, we uncover evidence for star forming material entrained in the outflow of the galaxy, and provide the first sub-kpc evidence for the receding side of the outflow.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Richard Rand

Second Committee Member

Jürgen Ott

Third Committee Member

Ylva Pihlström

Fourth Committee Member

Gregory Taylor

Keywords

Galaxies, Radio Astronomy, Molecular Lines, Interstellar Medium (ISM)

Document Type

Thesis

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