2010ApJ...718...37P -
Astrophys. J., 718, 37-42 (2010/July-3)
Weighing the galactic dark matter halo: a lower mass limit from the fastest halo star known.
PRZYBILLA N., TILLICH A., HEBER U. and SCHOLZ R.-D.
Abstract (from CDS):
The mass of the Galactic dark matter halo is under vivid discussion. A recent study by Xue et al. revised the Galactic halo mass downward by a factor of ∼2 relative to previous work, based on the line-of-sight velocity distribution of ∼2400 blue horizontal-branch (BHB) halo stars. The observations were interpreted with a statistical approach using cosmological galaxy formation simulations, as only four of the six-dimensional phase-space coordinates were determined. Here we concentrate on a close investigation of the stars with the highest negative radial velocity from that sample. For one star, SDSSJ153935.67+023909.8 (J1539+0239 for short), we succeed in measuring a significant proper motion, i.e., full phase-space information is obtained. We confirm the star to be a Population II BHB star from an independent quantitative analysis of the Sloan Digital Sky Survey (SDSS) spectrum–providing the first non-LTE (NLTE) study of any halo BHB star–and reconstruct its three-dimensional trajectory in the Galactic potential. J1539+0239 turns out to be the fastest halo star known to date, with a Galactic rest-frame velocity of 694+300 –221 km/s (full uncertainty range from Monte Carlo error propagation) at its current position. The extreme kinematics of the star allows a significant lower limit to be put on the halo mass in order to keep it bound, of Mhalo ≥ 1.7+2.3–1.1x1012 M☉. We conclude that the Xue et al. results tend to underestimate the true halo mass as their most likely mass value is consistent with our analysis only at a level of 4%. However, our result confirms other studies that make use of the full phase-space information.
Abstract Copyright:
∼
Journal keyword(s):
dark matter - Galaxy: halo - stars: atmospheres - stars: horizontal-branch - stars: kinematics and dynamics - stars: Population II
Simbad objects:
9
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2010ApJ...718...37P and select 'bookmark this link' or equivalent in the popup menu