CfA Colloquium Schedule Spring 2012
 16 February 2012

16 February 2012

Speaker: Tom Dame (CfA)

Title:The Milky Way as a Grand Design Spiral

Abstract:Although many grand design models of our Galaxy's spiral structure have been proposed over the past fifty years, unambiguous evidence for the type of two-fold symmetry expected of a barred spiral galaxy such as ours has remained elusive. In the far side of the Galaxy, spiral arms outside the solar circle are extremely distant and relatively deficient in molecular gas, and those within are largely masked by near-side material at the same velocity. A unique exception in the inner Galaxy is our recent identification of the Far 3-kpc Arm, its clear symmetry with respect to its near-side counterpart apparent only because of the large outward motions of both arms. We recently identified another far-side spiral arm in CO and H I, this one in the outer Galaxy at a distance of ~21 kpc. This arm appears to be the distant end of the prominent Scutum-Centaurus Arm and the symmetric counterpart of the nearby Perseus Arm. The discovery of both new arms will be described and discussed in the context of the large-scale structure of the Milky Way.

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