The cold veil of the Milky Way stellar halo
A. J. Deason (Cambridge), V. Belokurov (Cambridge), N. W. Evans, (Cambridge), S. E. Koposov (Cambridge), R. J. Cooke (Cambridge), J., Pe\~narrubia (Granada), C. F. P. Laporte (MPA), M. Fellhauer (Chile), M. G., Walker (Harvard), E. W. Olszewski (Arizona)

TL;DR
This study constructs a large sample of distant Milky Way halo stars using photometry and spectroscopy, revealing a surprisingly low mass estimate for the galaxy within 150 kpc based on stellar velocities.
Contribution
It provides the largest sample of individual star tracers out to 150 kpc and offers new insights into the Milky Way's mass distribution at large radii.
Findings
Radial velocity dispersion decreases with distance, indicating a cold halo at 100-150 kpc.
Mass within 150 kpc is estimated to be less than 10^12 solar masses.
The Milky Way's mass may be significantly lower than previously thought.
Abstract
We build a sample of distant (D > 80 kpc) stellar halo stars with measured radial velocities. Faint () candidate blue horizontal branch (BHB) stars were selected using the deep, but wide, multi-epoch Sloan Digital Sky Survey photometry. Follow-up spectroscopy for these A-type stars was performed using the VLT-FORS2 instrument. We classify stars according to their Balmer line profiles, and find 7 are bona fide BHB stars and 31 are blue stragglers (BS). Owing to the magnitude range of our sample, even the intrinsically fainter BS stars can reach out to D ~ 90 kpc. We complement this sample of A-type stars with intrinsically brighter, intermediate-age, asymptotic giant branch stars. A set of 4 distant cool carbon stars is compiled from the literature and we perform spectroscopic follow-up on a further 4 N-type carbon stars using the WHT-ISIS instrument. Altogether, this…
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Taxonomy
TopicsStellar, planetary, and galactic studies · Astronomy and Astrophysical Research · Astro and Planetary Science
