Status Report

One Ring to Encompass them All: A giant stellar structure that surrounds the Galaxy

By SpaceRef Editor
January 7, 2003
Filed under , ,

Astrophysics, abstract

From: Rodrigo Ibata <>
Date: Mon, 6 Jan 2003 16:28:45 GMT (602kb)

One Ring to Encompass them All: A giant stellar structure that surrounds
the Galaxy

R. A. Ibata,
M. J. Irwin,
G. F. Lewis,
A. M. N. Ferguson,
N. Tanvir

Comments: 6 pages, 6 (compressed) figures, submitted to MNRAS

We present evidence that the curious stellar population found by the Sloan
Digital Sky Survey in the Galactic anticentre direction extends to other
distant fields that skirt the plane of the Milky Way. New data, taken with the
INT Wide Field Camera show a similar population, narrowly aligned along the
line of sight, but with a Galactocentric distance that changes from ~15 kpc to
~20 kpc (over ~100 degrees on the sky). Despite being narrowly concentrated
along the line of sight, the structure is fairly extended vertically out of the
plane of the Disk, with a vertical scale height of 0.75+/-0.04 kpc. This
finding suggests that the outer rim of the Galaxy ends in a low-surface
brightness stellar ring. Presently available data do not allow us to ascertain
the origin of the structure. One possibility is that it is the wraith of a
satellite galaxy devoured long-ago by the Milky Way, though our favoured
interpretation is that it is a perturbation of the disk, possibly the result of
ancient warps. Assuming that the Ring is smooth and axisymmetric, the total
stellar mass in the structure may amount to 2×10^8 up to 10^9 Solar masses.

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