Skip navigation
Skip navigation

A Tale of Tidal Tails in the Milky Way

Casey, Andrew Raithby

Description

Hundreds of compact star systems encircle the Milky Way. Many of these systems have undergone partial disruption due to tidal forces, littering the halo with stellar streams. These tidal tails are sensitive to the Galactic potential, facilitating an excellent laboratory to investigate galaxy formation and evolution. To better understand the emergence of the Milky Way, this thesis examines the dynamics and chemistry of a number of known stellar streams. In particular the Sagittarius, Orphan and...[Show more]

dc.contributor.authorCasey, Andrew Raithby
dc.date.accessioned2019-02-18T23:44:43Z
dc.date.available2019-02-18T23:44:43Z
dc.date.copyright2014
dc.identifier.otherb3733011
dc.identifier.urihttp://hdl.handle.net/1885/156086
dc.description.abstractHundreds of compact star systems encircle the Milky Way. Many of these systems have undergone partial disruption due to tidal forces, littering the halo with stellar streams. These tidal tails are sensitive to the Galactic potential, facilitating an excellent laboratory to investigate galaxy formation and evolution. To better understand the emergence of the Milky Way, this thesis examines the dynamics and chemistry of a number of known stellar streams. In particular the Sagittarius, Orphan and Aquarius streams are investigated. Low-resolution spectra for hundreds of stars in the direction of the Virgo Over-Density and the Sagittarius northern leading arms have been obtained. Multiple significant kinematic groups are recovered in this accretion-dominated region, confirming detections by previous studies. A metal-poor population in the Sagittarius stream is discovered due to a photometric selection that was inadvertently biased towards more metal-poor stars. Positions and kinematics of Sagittarius stream members are compared with existing best-fitting dark matter models, and a tri-axial dark matter halo distribution is favoured. The Orphan stream is appropriately named, as no parent system has yet been identified. The stream has an extremely low surface brightness, which makes distinguishing stream members from field stars particularly challenging. From low-resolution spectra obtained for hundreds of stars, we identify likely Orphan stream red giant branch stars on the basis of velocity, metallicity, surface gravity, and proper motions. A negligible intrinsic velocity dispersion is found, and a wide spread in metallicities is observed, which suggests the undiscovered parent is similar to the present-day dwarf galaxies in the Milky Way. High-resolution spectra were obtained for five Orphan stream candidates, and the intrinsic chemical dispersion found from low-resolution spectra is confirmed from these data. Detailed chemical abundances for high-probability Orphan stream candidates further indicates a dwarf galaxy host. Low alpha-element abundance ratios are observed, and lower limits for [Ba/Y] are found, which sit well above the observed chemical evolution in the Milky Way. This thesis provides the first detailed chemical evidence for a dwarf galaxy origin, allowing us to rule out any association between the Orphan stream and the globular cluster NGC 2419. High-resolution, high signal-to-noise spectra for one third of the Aquarius stream have also been obtained. Contrary to previous work, there is no evidence that the Aquarius stream has resulted from a disrupted globular cluster. Detailed chemistry suggests that the Aquarius stars are galactic in origin, and not disrupted members from either a globular cluster or a dwarf galaxy. In the absence of compelling dynamic and/or chemical evidence to suggest otherwise, we advocate the `Aquarius Group' as a more appropriate description, and hypothesise that the moving group has resulted from a disk-satellite interaction on the order of a few billion years ago. The high-resolution spectra presented in this thesis has been analysed using custom written software. The software is designed to facilitate the transition between small and massive sample sizes, while ensuring data provenance, tangibility, and reproducibility. A detailed description of the software's graphical interface, capabilities and algorithms are presented, and future work is outlined.
dc.format.extentxv, 197 leaves
dc.titleA Tale of Tidal Tails in the Milky Way
dc.typeThesis (PhD)
local.description.notesThesis (Ph.D.)--Australian National University, 2014.
dc.date.issued2014
local.contributor.affiliationAustralian National University. Research School of Astronomy & Astrophysics
local.identifier.doi10.25911/5d514ef52aeff
dc.date.updated2019-01-10T03:25:12Z
local.mintdoimint
CollectionsOpen Access Theses

Download

File Description SizeFormat Image
b37330111_Casey_Andrew Raithby.pdf383.08 MBAdobe PDFThumbnail


Items in Open Research are protected by copyright, with all rights reserved, unless otherwise indicated.

Updated:  19 May 2020/ Responsible Officer:  University Librarian/ Page Contact:  Library Systems & Web Coordinator