Date of Graduation

5-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Kennefick, Daniel J.

Committee Member

Kennefick, Julia D.

Second Committee Member

Lehmer, Bret D.

Third Committee Member

Potra, Adriana

Keywords

Age gradients; Co-rotation radius; Density-Wave Theory; Spiral Galaxies; Star Formation History Maps; Stellar Clusters

Abstract

Studying galaxy structures using different wavebands enables us to observe a varietyof intrinsic galactic features and to test the validity of underlying theories in detail. Density wave theory, originally proposed by C.C. Lin and F. Shu (Lin & Shu 1964), explains the nature of the spiral arm patterns in disk galaxies as density waves that propagate through the galactic disk. From spiral galaxies to the rings of Saturn, density wave theory has had success in providing qualitative explanations of disk dynamics. However, it is now widely believed that galactic disks are dissipative systems which raises the question of whether they are really semi-permanent features as suggested by Lin and Shu. The question is when density waves do arise, how long are they sustained in this dissipative medium. Are they transient or relatively long-standing?. In this study I try to test the validity of density wave theory using multi-wavelength image data, star formation history maps and the spatially resolved stellar clusters. I also try to answer the question, whether transient or relatively long lasting spiral patterns better fit the patterns that we see in disk galaxies. The study primarily focuses on two implications of the theory, the co-rotation radius and the existence of an age-gradient. The work elaborates the use of multiple techniques in identifying the corotation radius and provides strong evidence in favor of density wave theory. Age gradients are observed using star formation history maps and specially resolved stellar cluster maps. The study investigates and presents evidence in favor of density wave theory framework and also provides a lower age limit for the spiral structure formation.

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