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Quantifying Kinematic Substructure in the Milky Way's Stellar Halo

Journal Article · · Astrophys.J.
 [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8];  [9];  [10];  [11];  [12];  [2];  [6];  [4];  [13]
  1. Joint Lab. of Optical Astron.; Heidelberg, Max Planck Inst. Astron.
  2. Heidelberg, Max Planck Inst. Astron.
  3. Fermilab
  4. Michigan State U.
  5. Michigan U.; Heidelberg, Max Planck Inst. Astron.
  6. Joint Lab. of Optical Astron.
  7. UC, Irvine
  8. Columbia U., CBA
  9. Case Western Reserve U.
  10. Lick Observ.
  11. Cambridge U.; Heidelberg, Max Planck Inst. Astron.; Sternberg Astron. Inst.
  12. Purple Mountain Observ.; Heidelberg, Max Planck Inst. Astron.
  13. New York U., CCPP
+ Show Author Affiliations
We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative 'close pair distribution' (CPD) as a statistic in the 4-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that are close in position on the sky tend to have more similar distances and radial velocities compared to a random sampling of these overall distributions. We make analogous mock-observations of 11 numerical halo formation simulations, in which the stellar halo is entirely composed of disrupted satellite debris, and find a level of substructure comparable to that seen in the actually observed BHB star sample. This result quantitatively confirms the hierarchical build-up of the stellar halo through a signature in phase (position-velocity) space. In detail, the structure present in the BHB stars is somewhat less prominent than that seen in most simulated halos, quite possibly because BHB stars represent an older sub-population. BHB stars located beyond 20 kpc from the Galactic center exhibit stronger substructure than at $$\rm r_{gc} < 20$$ kpc.
Research Organization:
Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Organization:
Sloan Digital Sky Survey
DOE Contract Number:
AC02-07CH11359
OSTI ID:
1974206
Report Number(s):
FERMILAB-PUB-10-466-AE-CD; arXiv:1011.1925; oai:inspirehep.net:876615
Journal Information:
Astrophys.J., Journal Name: Astrophys.J. Vol. 738
Country of Publication:
United States
Language:
English

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79 ASTRONOMY AND ASTROPHYSICS