Alabama_May2018_Erwin_Rings-and-Breaks_export.pdf (2.16 MB)

(Outer) Rings and Breaks in Disk Galaxy Profiles

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posted on 01.06.2018 by Erwin, Peter

I discuss what is currently known about connections between outer rings and the underlying radial profiles of galactic disks. Correlations between rings and truncations (Type II profiles, with downbending breaks in the surface-brightness profile) allow us to distinguish between two general models of profile formation. In many early-type disk galaxies, outer rings coincide with downbending breaks, suggesting that ring formation is directly linked to break formation, most likely due to an outer Lindblad resonance. But outer rings also coexist with Type I profiles (where no break is present), and in some cases with Type II profiles where the break is well outside the ring; the latter are indications that many truncations, especially in late-type spirals, are due to a different mechanism, such as a star-formation threshold. I will also discuss how rings can potentially produce false breaks in Type I profiles, especially in edge-on galaxies, as well as potential connections between outer rings and anti-truncated (Type III) profiles.