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Title: Touching the void: A striking drop in stellar halo density beyond 50 kpc

We use A-type stars selected from Sloan Digital Sky Survey data release 9 photometry to measure the outer slope of the Milky Way stellar halo density profile beyond 50 kpc. A likelihood-based analysis is employed that models the ugr photometry distribution of blue horizontal branch and blue straggler stars. In the magnitude range 18.5 < g < 20.5, these stellar populations span a heliocentric distance range of: 10 ≲ D {sub BS}/kpc ≲ 75, 40 ≲ D {sub BHB}/kpc ≲ 100. Contributions from contaminants, such as QSOs, and the effect of photometric uncertainties, are also included in our modeling procedure. We find evidence for a very steep outer halo profile, with power-law index α ∼ 6 beyond Galactocentric radii r = 50 kpc, and even steeper slopes favored (α ∼ 6-10) at larger radii. This result holds true when stars belonging to known overdensities, such as the Sagittarius stream, are included or excluded. We show that, by comparison to numerical simulations, stellar halos with shallower slopes at large distances tend to have more recent accretion activity. Thus, it is likely that the Milky Way has undergone a relatively quiet accretion history over the past several gigayears. Our measurement of themore » outer stellar halo profile may have important implications for dynamical mass models of the Milky Way, where the tracer density profile is strongly degenerate with total mass estimates.« less
Authors:
;  [1] ; ;  [2]
  1. Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA 95064 (United States)
  2. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
Publication Date:
OSTI Identifier:
22356859
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DENSITY; DISTRIBUTION; MASS; MILKY WAY; PHOTOMETRY; STARS