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The Astrophysical Journal
Article . 2014 . Peer-reviewed
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https://dx.doi.org/10.48550/ar...
Article . 2014
License: arXiv Non-Exclusive Distribution
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ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION

Authors: Joss Bland-Hawthorn; Prajwal R. Kafle; Prajwal R. Kafle; Sanjib Sharma; Geraint F. Lewis;

ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION

Abstract

Halo stars orbit within the potential of the Milky Way and hence their kinematics can be used to understand the underlying mass distribution. However, the inferred mass distribution depends sensitively upon assumptions made on the density and the velocity anisotropy profiles of the tracers. Also, there is a degeneracy between the parameters of the halo and that of the disk or bulge. Here, we decompose the Galaxy into bulge, disk and dark matter halo and then model the kinematic data of the halo BHB and K-giants from the SEGUE. Additionally, we use the gas terminal velocity curve and the Sgr A$^*$ proper motion. With $R_\odot = 8.5$kpc, our study reveals that the density of the stellar halo has a break at $17.2^{+1.1}_{-1.0}$ kpc, and an exponential cut-off in the outer parts starting at $97.7^{+15.6}_{-15.8}$kpc. Also, we find the velocity anisotropy is radially biased with $��_s= 0.4\pm{0.2}$ in the outer halo. We measure halo virial mass $M_{\text{vir}} = 0.80^{+0.31}_{-0.16} \times 10^{12} M_{\odot}$, concentration $c=21.1^{+14.8}_{-8.3}$, disk mass of $0.95^{+0.24}_{-0.30}\times10^{11} M_{\odot}$, disk scale length of $4.9^{+0.4}_{-0.4}$ kpc and bulge mass of $0.91^{+0.31}_{-0.38} \times 10^{10} M_{\odot}$. The mass of halo is found to be small and this has important consequences. The giant stars reveal that the outermost halo stars have low velocity dispersion interestingly suggesting a truncation of the stellar halo density rather than a small overall mass of the Galaxy. Our estimates of local escape velocity $v_{\rm esc} = 550.9^{+32.4}_{-22.1}$ kms$^{-1}$ and dark matter density $��^{\rm DM}_{\odot} = 0.0088^{+0.0024}_{-0.0018} M_{\odot} {\rm pc^{-3}} $ ($0.35^{+0.08}_{-0.07}$ GeV cm$^{-3}$) are in good agreement with recent estimates. Some of the above estimates are depended on the adopted value of $R_\odot$ and of outer power-law index of the tracer number density.

Accepted for publication in ApJ

Keywords

Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
182
Top 1%
Top 10%
Top 1%
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