The relation between atomic and molecular gas: the Magellanic Clouds and beyond

In this thesis, I employ two different observational techniques, ultraviolet spectroscopy and radio interferometry imaging, to study the atomic and molecular gas relation in the Large/Small Magellanic Clouds and 43 nearby galaxies. These galaxies demonstrate various galactic environments compared with the Milky Way and provide an ideal sample for testing the cloud-scale and galactic-scale models of the atomic-to-molecular transition and molecular cloud formation. From the absorption line analysis on archival data provided by the Far Ul- traviolet Spectroscopic Explorer, I found the molecular hydrogen absorbers trace the diffuse and translucent cloud components in the Magellanic Clouds. Although the absorbers’ veloc- ities generally agree with the large-scale kinematic structure revealed in HI 21cm emission, their physical properties are distinct from the gas revealed by the molecular gas emission in CO. The observed atomic-to-molecular gas relation derived from the absorbers, together with existing gas cloud models, suggest the possible existence of significant diffuse warm atomic gas along the ultraviolet absorption sight lines. In the second part of the thesis, I use high-resolution CO and HI 21cm observations of 45 nearby galaxies, including the Magel- lanic clouds, to analyze the spatial correlation of the interstellar gas in molecular and atomic phases and old stellar populations. The results suggest strong independent roles for galaxy metallicity and stellar-to-gas ratios in the atomic-to-molecular gas transition and are consis- tent with a self-regulation galaxy model of star formation and interstellar medium evolution. The model and observations highlight the importance of the diffuse atomic gas component in understanding the observed atomic and molecular gas relation at sub-kiloparsec and kilo- parsec scales. I conclude that it is essential to incorporate diffuse cloud components into theoretical models of galaxy ISM evolution and molecular cloud formation because of their important role in the galactic ecosystem.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Astronomy

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Xue, Rui

Contributors dc:contributor

• Wong, Tony
• ISM
• Chu, You-Hua
• Looney, Leslie W.
• Welty, Daniel

• Galaxies
• Interstellar Medium (ISM)

Statement dc:rights

• Copyright 2015 Rui Xue

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/88236

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/88236