2003/01/31 by B. Yanny, Brian Yanny, Heidi Jo Newberg +22 · 3 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/374220
published as Astrophys.J. 588 (2003) 824; Erratum-ibid. 605 (2004) 575-577 · Revised to include 2 page erratum (appended to original paper), 18 pages, Latex, 12 figures (3 revised), for data table: choose 'other formats', download source to find table1rev.txt
openalex publication_date 2003/05/10 · arxiv created 2003/12/19 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
We present evidence for a ring of stars in the plane of the Milky Way, extending at least from l = 180° to 227° with turnoff magnitude g ~ 19.5; the ring could encircle the Galaxy. We infer that the low Galactic latitude structure is at a fairly constant distance of R = 18 ± 2 kpc from the Galactic center above the Galactic plane and has R = 20 ± 2 kpc in the region sampled below the Galactic plane. The evidence includes 500 Sloan Digital Sky Survey spectroscopic radial velocities of stars within 30° of the plane. The velocity dispersion of the stars associated with this structure is found to be 27 km s -1 at ( l , b ) = (198°, - 27°), 22 km s -1 at ( l , b ) = (225°, 28°), 30 km s -1 at ( l , b ) = (188°, 24°), and 30 km s -1 at ( l , b ) = (182°, 27°). The structure rotates in the same prograde direction as the Galactic disk stars but with a circular velocity of 110 ± 25 km s -1 . 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 -1 at ( l , b ) = (165°, - 55°). We estimate a preliminary metallicity from the Ca II (K) line and color of the turnoff stars of [Fe/H] = -1.6 with a dispersion of 0.3 dex and note that the turnoff color is consistent with that of the spheroid population. We interpret our measurements as evidence for a tidally disrupted satellite of 2 × 10 7 to 5 × 10 8 M ☉ that rings the Galaxy.