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Metallicity Map of M33 Open Access


Other title
abundance gradient
Galaxy M33
Type of item
Degree grantor
University of Alberta
Author or creator
Koning, Alice H.
Supervisor and department
Rosolowsky, Erik (Physics)
Examining committee member and department
Sydora, Richard (Physics)
Sivakoff, Gregory (Physics)
Rosolowsky, Erik (Physics)
Heinke, Craig (Physics)
Department of Physics

Date accepted
Graduation date
Master of Science
Degree level
I use Keck I spectroscopic observations of 701 Hα sources in the nearby spiral galaxy M33 to determine oxygen, nitrogen, sulfur, and neon abundances in HII regions across the face of the galactic disk. Abundance measurements are obtained with two separate methods (PyNeb and NEAT) through the use of the only known direct metallicity determination method, which relies on detections of weak, temperature-sensitive auroral lines. This data set is approximately double the size of any previous HII region metallicity study in M33. Reliable oxygen abundances are determined for 88 HII regions with PyNeb, and 108 HII regions with NEAT (with significant overlap between the two samples). I investigate the temperature and density distributions, as well as the relation between strong-line metallicity indicators and the metallicity derived from weak auroral lines. I plot radial abundance gradients for [O/H], [N/H], [NII/OII], [S/H], [S/O], [Ne/H], and [Ne/O]. The [O/H] gradient has more scatter than the [N/H] gradient, although both show clear signs of decreasing abundances with increasing galactic radius. The [NII/OII] gradient supports previous evidence that the nitrogen abundance falls off more rapidly than oxygen at larger radii. Conversely, the [Ne/O] gradient indicates that neon falls off more slowly than oxygen at larger radii. The sulfur radial gradient is consistent with a flat slope. I present 2D metallicity maps for [O/H], [N/H], and [NII/OII]. The [O/H] map indicates significant azimuthal fluctuations across the disk of M33, although it is uncertain whether the dominant factor is true azimuthal structure or the relatively large uncertainties on the oxygen abundance measurements. The [N/H] and [NII/OII] abundance maps are much smoother than the [O/H] map.
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File title: Introduction
File title: M33 Metallicity Map, M. Sc. Thesis
File author: Alice H. Koning
Page count: 140
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