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, Masataka Fukugita, Željko Ivezic, Don Q. Lamb, Donald P. Schneider, Donald G. York

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Abstract

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 × 107 to 5 × 10 8 M that rings the Galaxy.

Original languageEnglish (US)
Pages (from-to)824-841
Number of pages18
JournalAstrophysical Journal
Volume588
Issue number2 I
DOIs
Publication statusPublished - May 10 2003

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All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Yanny, B., Newberg, H. J., Grebel, E. K., Kent, S., Odenkirchen, M., Rockosi, C. M., ... York, D. G. (2003). A low-latitude halo stream around the Milky Way. Astrophysical Journal, 588(2 I), 824-841. https://doi.org/10.1086/374220