Astrophysics, abstract
astro-ph/0605728

From: Evan Levine [view email]

Date: Tue, 30 May 2006 20:06:03 GMT (595kb)

The Spiral Structure of the Outer Milky Way in Hydrogen

Authors: E.S. Levine, Leo Blitz, Carl Heiles

Comments: 10 pages with 4 color figures. Accepted for publication in Science. Embargoed for discussion in the popular press until publication in ScienceXpress. Higher resolution versions of figures 3 and 4 are available at this http URL

We produce a detailed map of the perturbed surface density of neutral hydrogen in the outer Milky Way disk demonstrating that the Galaxy is a non-axisymmetric multi-armed spiral. Spiral structure in the southern half of the Galaxy can be traced out to at least 25 kpc, implying a minimum radius for the gas disk. Overdensities in the surface density are coincident with regions of reduced gas thickness. The ratio of the surface density to the local median surface density is relatively constant along an arm. Logarithmic spirals can be fit to the arms with pitch angles of 20-25 degrees.

http://arxiv.org/abs/astro-ph/0605728