THE SEGUE K GIANT SURVEY. III. QUANTIFYING GALACTIC HALO SUBSTRUCTURE

William Janesh, Heather L. Morrison, Zhibo Ma, Constance Rockosi, Else Starkenburg, Xiang Xiang Xue, Hans Walter Rix, Paul Harding, Timothy C. Beers, Jennifer Johnson, Young Sun Lee, Donald P. Schneider

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22 Scopus citations

Abstract

We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125 kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (∼33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.

Original languageEnglish (US)
Article number80
JournalAstrophysical Journal
Volume816
Issue number2
DOIs
StatePublished - Jan 10 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Janesh, W., Morrison, H. L., Ma, Z., Rockosi, C., Starkenburg, E., Xue, X. X., Rix, H. W., Harding, P., Beers, T. C., Johnson, J., Lee, Y. S., & Schneider, D. P. (2016). THE SEGUE K GIANT SURVEY. III. QUANTIFYING GALACTIC HALO SUBSTRUCTURE. Astrophysical Journal, 816(2), [80]. https://doi.org/10.3847/0004-637X/816/2/80