Secular Evolution in Late-Type Spiral Galaxies

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Title: Secular Evolution in Late-Type Spiral Galaxies
Creators: Wong, Man-Hong
Advisor: Martini, Paul
Issue Date: 2010-06
Abstract: Galaxy evolution through internal rather than external processes is known as secular evolution. Evidence for secular evolution comes in various forms, most notably the development of a pseudobulge. Pseudobulges differ from merger-built bulges because they exhibit disk-like features. While the bulges of most spirals are best-fit by a Sersic surface brightness profile with index n = 4 (also known as a de Vaucouleurs r1/4 profile), pseudobulges typically have n = 1 − 3, where an n = 1 Sersic profile corresponds to a second exponential profile (in addition to the disk itself). We used the exponential surface brightness profile of pseudobulges to identify these components in our sample of 20 late-type spiral galaxies. Late-type disks are well-suited to study signs of secular evolution because any past interactions and mergers would have developed at least a small bulge and changed their classification. There is evidence that more massive disk galaxies may be more likely to drive mass inwards and produce a pseudobulge. We perform decompositions of the galaxies to find these features. We also study the the concentrations of polycyclic aromatic hydrocarbons (PAHs) as a function of mass because they have been shown to trace molecular gas, which is the fuel needed to form the stars that make up a pseudobulge. NGC2805, a lower-mass galaxy, was the only galaxy in our sample that has a pseudobulge. We also found no correlation between the central concentration of PAH emission and the mass. This implies that more massive galaxies are not more efficient at driving gas inwards.
Embargo: No embargo
Series/Report no.: The Ohio State University. Department of Astronomy Honors Theses; 2010
Keywords: astronomy
secular evolution
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