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Title: Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these interactions in the form of stellar streams, substructures, and chemically distinct stellar components. The impact of dwarf galaxy mergers on the content and morphology of the Galactic disk is still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups, which may have extragalactic origin. However, there is mounting evidence that stellar overdensities at the outer disk/halo interface could have been caused by the interaction of a dwarf galaxy with the disk. Here we report detailed spectroscopic analysis of 14 stars drawn from two stellar overdensities, each lying about 5 kiloparsecs above and below the Galactic plane - locations suggestive of association with the stellar halo. However, we find that the chemical compositions of these stars are almost identical, both within and between these groups, and closely match the abundance patterns of the Milky Way disk stars. This study hence provides compelling evidence that these stars originate from the disk and the overdensities they are part of were createdmore » by tidal interactions of the disk with passing or merging dwarf galaxies.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ORCiD logo [6] ;  [7] ;  [8] ;  [8] ;  [9] ;  [10] ;  [11]
  1. Max Planck Institute for Astronomy, Heidelberg (Germany)
  2. Deutsche Borse AG, Eschborn (Germany)
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  4. Institute of Space Sciences (ICE, CSIC), Barcelona (Spain); Institut d'Estudis Espacials de Catalunya (IEEC), Barcelona (Spain)
  5. LaGuardia Community College, City Univ. of New York, Long Island City, NY (United States)
  6. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  7. The Australian National Univ., Canberra, ACT (Australia); ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) (Australia)
  8. Columbia Univ., New York, NY (United States)
  9. Princeton Univ., Princeton, NJ (United States)
  10. Univ. of Oxford, Oxford (United Kingdom)
  11. Max Planck Institute for Astronomy, Heidelberg (Germany); Korea Astronomy and Space Science Institute, Daejon (South Korea); The Ohio State Univ., Columbus, OH (United States)
Publication Date:
Report Number(s):
arXiv:1803.00563; FERMILAB-PUB-18-155-AE
Journal ID: ISSN 0028-0836; 1671455
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Name: Nature (London); Journal Volume: 555; Journal Issue: 7696; Journal ID: ISSN 0028-0836
Nature Publishing Group
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
OSTI Identifier: