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Dissertation/Thesis Abstract

Neutral interstellar medium phases and star formation tracers in dwarf galaxies
by Cigan, Phillip Johnathan, Ph.D., New Mexico Institute of Mining and Technology, 2015, 229; 3718424
Abstract (Summary)

Dwarf galaxies present interesting observational challenges for the studies of various galaxy properties: despite their abundance and proximity to the Milky Way, they typically have very low surface brightnesses and small physical sizes. Until now, only the extreme variety of dwarfs — those undergoing strong bouts of star formation — have been observed in the FIR, due to observational difficulties. However, this population does not represent the majority of dwarfs, which have only moderate star formation rates and extremely low metallicity (the fraction of heavy elements to hydrogen). The advent of the Herschel Space Telescope, with its superior resolution and sensitivity over previous generations of telescopes, has made it possible to measure FIR spectral lines and broadband continuum in normal dwarf galaxies, expanding the scope of studies beyond the brighter, but more extreme, varieties.

The general goal of my research was to study the conditions in the interstellar media (ISM) of typical dwarf galaxies. The LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, TheHI Nearby Galaxy Survey) project aims to unravel many mysteries of nearby dwarfs using a suite of multi-wavelength data, and the new additions from Herschel help provide insight into the physics of these systems. I reduced and analyzed FIR fine-structure spectral line data for the LITTLE THINGS sample to study the different phases of the ISM, as well as FIR photometry data to access the dust properties and infrared continuum emission in these systems. The FIR spectral lines are diagnostics for the conditions in the ISM of galaxies, telling us about heating efficiency, the fraction of gas that resides in photodissociation regions (PDRs), abundance of highly ionized gas from massive stars, and other physical descriptions. The photometric continuum observations enable the modeling of interstellar dust properties – dust plays an important role in shielding and cooling molecular clouds which form stars, as well as heating via the photoelectric effect. I also utilized neutral hydrogen data to probe the neutral medium in relation to the FIR, as well as optical and UV data to characterize star formation and the emission of starlight.

Indexing (document details)
Advisor: Young, Lisa
Commitee: Meier, David, Westpfahl, David, Wrobel, Joan
School: New Mexico Institute of Mining and Technology
Department: Astrophysics
School Location: United States -- New Mexico
Source: DAI-B 76/12(E), Dissertation Abstracts International
Subjects: Astrophysics, Physics, Astronomy
Keywords: Dust, Dwarf galaxies, Galaxies, Infrared, Interstellar medium, Metallicity
Publication Number: 3718424
ISBN: 978-1-321-98236-7
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