Persistent Link:
http://hdl.handle.net/10150/202752
Title:
The Outer Disks of Nearby Galaxies
Author:
Herbert-Fort, Stephane
Issue Date:
2011
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This dissertation presents three observational projects designed to characterize the outer disks of nearby galaxies (beyond the optical radius R₂₅). Until very recently, outer disks remained an elusive and poorly-understood component of disk galaxies. We first present a Large Binocular Telescope (LBT) optical imaging survey of nearby outer disks to examine the basic properties of this component. Our LBT observations indicate that most nearby galaxies host an outer disk with star formation occurring at a very low level. We detect hundreds of outer disk star clusters and show that they typically have masses ∼ 10² − 10⁴M⊙ and ages up to a Gyr. The clusters are born in groups that can remain clustered for a Gyr or more, while the clusters slowly evaporate stars into a diffuse stellar component. The clusters appear to form from localized overdensities in the gas distribution primarily associated with spiral structure. The clusters extend to 2R₂₅ in our sample. We find that some clusters may also reside well outside of their host galaxy’s gas disk. Our second project is a kinematic study of Hɑ knots in the outer disk of the large, isolated, face-on galaxy NGC 628, using Inamori Magellan Areal Camera and Spectrograph (IMACS) observations from the Magellan telescope. This galaxy shows a kinematically cold outer disk (velocity dispersion < 11 km s⁻¹) with a mass density ∑ = 7.5 M⊙ pc⁻². Our observations cannot exclude uniform star formation lasting a Hubble time in this outer disk and confirm that this component is an extension of the kinematically-cold inner disk. Our third project is a search for molecular emission in the outer disk of NGC 628, using the sensitive Atacama LargeMillimeter Array (ALMA) receiver on the Submillimeter Telescope (SMT). We did not detect emission from our outer disk pointings, though we are able to provide useful estimates for future ALMA observations of outer disk knots. Our SMT observations indicate that the H₂ / H I ratio is ∼ 100× lower in the outer disk than in the inner disk, which likely explains, at least in part, the trend towards smaller clusters and lower star formation rates at larger radii.
Type:
text; Electronic Dissertation
Keywords:
galaxies; outer; populations; structure; Astronomy; cluster; disk
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Astronomy
Degree Grantor:
University of Arizona
Advisor:
Zaritsky, Dennis

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleThe Outer Disks of Nearby Galaxiesen_US
dc.creatorHerbert-Fort, Stephaneen_US
dc.contributor.authorHerbert-Fort, Stephaneen_US
dc.date.issued2011-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis dissertation presents three observational projects designed to characterize the outer disks of nearby galaxies (beyond the optical radius R₂₅). Until very recently, outer disks remained an elusive and poorly-understood component of disk galaxies. We first present a Large Binocular Telescope (LBT) optical imaging survey of nearby outer disks to examine the basic properties of this component. Our LBT observations indicate that most nearby galaxies host an outer disk with star formation occurring at a very low level. We detect hundreds of outer disk star clusters and show that they typically have masses ∼ 10² − 10⁴M⊙ and ages up to a Gyr. The clusters are born in groups that can remain clustered for a Gyr or more, while the clusters slowly evaporate stars into a diffuse stellar component. The clusters appear to form from localized overdensities in the gas distribution primarily associated with spiral structure. The clusters extend to 2R₂₅ in our sample. We find that some clusters may also reside well outside of their host galaxy’s gas disk. Our second project is a kinematic study of Hɑ knots in the outer disk of the large, isolated, face-on galaxy NGC 628, using Inamori Magellan Areal Camera and Spectrograph (IMACS) observations from the Magellan telescope. This galaxy shows a kinematically cold outer disk (velocity dispersion < 11 km s⁻¹) with a mass density ∑ = 7.5 M⊙ pc⁻². Our observations cannot exclude uniform star formation lasting a Hubble time in this outer disk and confirm that this component is an extension of the kinematically-cold inner disk. Our third project is a search for molecular emission in the outer disk of NGC 628, using the sensitive Atacama LargeMillimeter Array (ALMA) receiver on the Submillimeter Telescope (SMT). We did not detect emission from our outer disk pointings, though we are able to provide useful estimates for future ALMA observations of outer disk knots. Our SMT observations indicate that the H₂ / H I ratio is ∼ 100× lower in the outer disk than in the inner disk, which likely explains, at least in part, the trend towards smaller clusters and lower star formation rates at larger radii.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectgalaxiesen_US
dc.subjectouteren_US
dc.subjectpopulationsen_US
dc.subjectstructureen_US
dc.subjectAstronomyen_US
dc.subjectclusteren_US
dc.subjectdisken_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineAstronomyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorZaritsky, Dennisen_US
dc.contributor.committeememberWalker, Christopheren_US
dc.contributor.committeememberDavé, Romeelen_US
dc.contributor.committeememberRieke, Marciaen_US
dc.contributor.committeememberNarayanan, Desikaen_US
dc.contributor.committeememberZaritsky, Dennisen_US
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