Date of Award

Summer 6-5-2014

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysical & Planetary Sciences

First Advisor

Jason Glenn

Second Advisor

John Bally

Third Advisor

Julie Comerford

Abstract

Molecular gas is the raw material of star formation. The 12CO J=1→0 line is well known to trace the bulk of the cool molecular gas in the interstellar medium of nearby galaxies. New data from the Herschel Space Observatory, however, indicates that higher-energy CO rotational lines (e.g. CO J=6→5) are emitted from significantly warmer molecular gas. Studying this warmer, more luminous gas can provide useful clues for understanding the excitation of molecular gas by star formation.

This work establishes a pipeline to simultaneously model the physical conditions of cool and warm CO gas using the CO spectral line energy distributions from J=1→0 to J=13→12. We confirm that, in a variety of galaxies, CO is emitted from a low-pressure/high-mass component traced by the low-J lines and a high-pressure/low-mass component that dominates the luminosity. An initial survey of 17 infrared-luminous galaxy systems observed by the Herschel-SPIRE Fourier Transform Spectrometer (FTS) investigates how the physical properties and excitation mechanisms of the warm/cool CO vary with total infrared luminosity, dust mass, atomic fine-structure emission, and more. This work includes an in-depth discussion of the systematic effects of two-component CO modeling as well as comparisons of the derived physical conditions to those of Galactic star-forming regions and high-redshift submillimeter galaxies.

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