Article

The Ghost of Sagittarius and Lumps in the Halo of the Milky Way

Heidi Jo NewbergDepartment of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180Brian YannyEqual first authorsConnie RockosiDepartment of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637Eva K. GrebelMax-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, GermanyHans‐Walter RixMax-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, GermanyJon BrinkmannIstvan CsabaiDepartment of Physics and Complex Systems, Eötvös Loránd University, Pazmany Peter setany 1/A, H-1117 Budapest, HungaryGreg HennessyUS Naval Observatory, 3450 Massachusetts Avenue NW, Washington, DC 20392-5420Robert B. HindsleyUS Naval Observatory, 3450 Massachusetts Avenue NW, Washington, DC 20392-5420Rodrigo IbataUniversity of Strasbourg, 67000 Strasbourg, FranceZeljko IvezićPrinceton University Observatory, Princeton, NJ 08544Don LambDepartment of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637E. Thomas NashFermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510Michael OdenkirchenMax-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, GermanyHeather A. RaveDepartment of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180D. P. SchneiderDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802J. Allyn SmithDepartment of Physics and Astronomy, University of Wyoming, P.O. Box 3905, Laramie, WY 82071Andrea StolteMax-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, GermanyDonald G. YorkDepartment of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637

2002en

ABI

Abstract

We identify new structures in the halo of the Milky Way from positions, colors, and magnitudes of five million stars detected in the Sloan Digital Sky Survey. Most of these stars are within 1.degrees26 of the celestial equator. We present color-magnitude diagrams (CMDs) for stars in two previously discovered, tidally disrupted structures. The CMDs and turnoff colors are consistent with those of the Sagittarius dwarf galaxy, as had been predicted. In one direction, we are even able to detect a clump of red stars, similar to that of the Sagittarius dwarf, from stars spread across 110 deg(2) of sky. Focusing on stars with the colors of F turnoff objects, we identify at least five additional overdensities of stars. Four of these may be pieces of the same halo structure, which would cover a region of the sky at least 40 in diameter, at a distance of 11 kpc from the Sun (18 kpc from the center of the Galaxy). The turnoff is significantly bluer than that of thick-disk stars, yet the stars lie closer to the Galactic plane than a power-law spheroid predicts. We suggest two models to explain this new structure. One possibility is that this new structure could be a new dwarf satellite of the Milky Way, hidden in the Galactic plane and in the process of being tidally disrupted. The other possibility is that it could be part of a disklike distribution of stars which is metal-poor, with a scale height of approximately 2 kpc and a scale length of approximately 10 kpc. The fifth overdensity, which is 20 kpc away, is some distance from the Sagittarius dwarf streamer orbit and is not associated with any known Galactic structure. We have tentatively identified a sixth overdensity in the halo. If this sixth structure is instead part of a smooth distribution of halo stars (the spheroid), then the spheroid must be very flattened, with axial ratio q = 0.5. It is likely that there are many smaller streams of stars in the Galactic halo.

Identifiers

DOI: 10.1086/338983

Citations and references

Cited by 20 references

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