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A Low Latitude Halo Stream around the Milky Way

By SpaceRef Editor
January 6, 2003
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Astrophysics, abstract

From: Brian Yanny <>
Date: Thu, 2 Jan 2003 23:04:41 GMT (314kb)

A Low Latitude Halo Stream around the Milky Way

Brian Yanny,
Heidi Jo Newberg,
Eva K. Grebel,
Steve Kent,
Michael Odenkirchen,
Connie M. Rockosi,
David Schlegel,
Mark Subbarao,
Jon Brinkmann,
Zeljko Ivezic,
Don Q. Lamb,
Donald P. Schneider

Comments: Submitted to ApJ, 32 pages, Latex, 12 figures

We present evidence for a ring of stars in the plane of the Milky Way,
extending at least from l = 180 deg to l = 227 deg; the ring could encircle the
Galaxy. The low Galactic latitude structure is at a fairly constant distance of
$R = 18 pm 2$ kpc from the Galactic Center above the Galactic plane, and has
$R = 20 pm 2$ kpc in the region sampled below the Galactic plane. The evidence
includes five hundred SDSS spectroscopic radial velocities of stars within 30
deg of the plane. The velocity dispersion of the stars associated with this
structure is found to be 27 km/s at (l,b) = (198,-27), 22 km/s at (l,b) = (225,
28), 30 km/s at (l,b) = (188, 24), and 30 km/s at (l,b) = (182, 27) degrees.
The structure co-rotates with the Galactic disk stars at $110 pm 25$ km/s. The
narrow measured velocity dispersion is inconsistent with power law spheroid or
thick disk populations. We compare the velocity dispersion in this structure
with the velocity dispersion of stars in the Sagittarius dwarf galaxy tidal
stream, for which we measure a velocity dispersion of 20 km/s at (l,b) = (165,
-55) degrees. We interpret our measurements as evidence for a tidally disrupted
satellite of $2 imes 10^7$ to $5 imes 10^8$ solar masses which rings the

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