Gravitational torques of the dust penetrated stellar backbone of extragalactic spiral disks
Date
2008-06-24T12:11:43Z
Authors
Groess, Robert
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Abstract
“The nature of the nebulae and their place in the scheme of the universe have been
favorite subjects of controversy since the very dawn of telescopic observations. In these
later days, when the non-galactic nebulae have been clearly differentiated from the
diffuse and the planetary, the discussion has concentrated around the spectacular forms
of the spirals… island universes, scattered through the remote depths of space.”
– Edwin P. Hubble
It was only a mere 45 years ago, that some of the foremost astronomers such as Allan
Sandage and Donald Lynden Bell believed that spiral galaxies were monolithic islands
which were dynamically closed. This thesis has awaited the dawning of a new era
wherein the disks of spiral galaxies can be “dust penetrated”. Prevalent ideas in the
literature are overturned. Unprecedented images from IRAC onboard the Spitzer Space
Telescope reveal the dynamic nature of nearby disk galaxies, including the two dominant
spirals in our Local Group beyond the Milky Way. We show that M33 is a spiral galaxy
whose disk grows outwards with time and which serves as a local Rosetta stone of a
dynamically open system. We next show that the present-day morphology of M31 was
induced only 210 million years ago. IRAC images betray its tumultuous recent past with
the presence of two spectacular off-centre rings of dust, glowing at 8.0μm. A collision
scenario seems most likely, with one of its larger satellite galaxies, M32. In our local
universe, the bar phenomenon is ubiquitous. We separate bars from their parent disks in a
sample of about 40 spiral galaxies, revealing that stronger spirals are not necessarily
driven by stronger bars. Bars are not the universal excitation mechanism by which spiral
structure is induced. Finally, surprising insights are gleaned from the IRAC 8.0μm
window pertaining to the dust morphology of barred spirals. Three distinct form families
of stellar bars are presented. May this thesis serve as “one small step for man” in our
quest to expand our knowledge in the new epoch of quantitative galaxy classification in
the dust-penetrated regime.
Description
Keywords
Nebulae, Galaxies