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

By P. Kafle, Sanjib Sharma, Geraint F. Lewis, Joss Bland-Hawthorn. 2014

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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 on assumptions made on the density and the velocity anisotropy profiles of the tracer population. Also, there is a degeneracy between the parameters of the halo and those of the disk or bulge. Most previous attempts that use halo stars have made arbitrary assumptions about these. In this paper, we decompose the Galaxy into three major components—a bulge, a Miyamoto–Nagai disk, and a Navarro–Frenk–White dark matter halo – and then model the kinematic data of the halo blue horizontal branch and K-giant stars from the Sloan Extension for Galactic Understanding and Exploration. Additionally, we use the gas terminal velocity curve and the Sgr A* proper motion. With the distance of the Sun from the center of the Galaxy R☉ = 8.5 kpc, our kinematic analysis reveals that the density of the stellar halo has a break at and an exponential cutoff in the outer parts starting at . Also, we find that the tracer velocity anisotropy is radially biased with βs = 0.4 ± 0.2 in the outer halo. We measure halo virial mass Mvir to be , concentration c to be , disk mass to be , disk scale length to be , and bulge mass to be . The halo mass is found to be small, and this has important consequences. The giant stars reveal that the outermost halo stars have low velocity dispersion, but interestingly this suggests a truncation of the stellar halo density rather than a small overall mass of the Galaxy. Our estimates of local escape velocity and dark matter density ( GeV cm−3) are in good agreement with recent estimates. Some of the above estimates, in particular Mvir, are dependent on the adopted value of R☉ and also on the choice of the outer power-law index of the tracer number density.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/47ca392c7a44748408b45da40c1ee6e240690970

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Citations in the corpus

The mass distribution and gravitational potential of the Milky Way (2016, methodology): “Kafle et al.(2014) use similar techniques to this paper (and Paper I) to determine a best fitting mass model for the Milky Way as a whole, taking into account many constraints.”
The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution (2016, methodology): “However, as argued by Kafle et al. (2014) and Piffl et al. (2014), the theoretical relation is constructed from simulations with dark matter only.”
The ORGAN Experiment: An axion haloscope above 15 GHz (2017, methodology): “ing the inverse of equation 2 over the frequency range and solving for g a inputting a xed value of measurement time, with a signal to noise ratio of 5, assuming a dark matter density of 0:45 GeV cm3 [35]. Stage II During the operation of Stage I the ORGAN collaboration plans to prototype and develo”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, methodology): “F or p er so na l u se o nl y. et al. (2002) and Kafle et al. (2014), where ρvir = vir Mρcrit ( vir = 340) such that rvir = 258 ( vir M 102 )−1/3 ( M vir 1012 M )1/3 kpc. (3) Because the mass enclosed depends on the product vir M, our values are within 5% of estimators that use ( vir, M) = (360,…”
The milky way total mass profile as inferred from Gaia DR2 (2019, methodology): “…the analysis in the same spirit as Dehnen & Binney (1998, see also Klypin et al. 2002; Weber & de Boer 2010; McMillan 2011; Bovy et al. 2012; Kafle et al. 2014; McMillan 2017), that is, we estimate the best fitting MW mass model by varying several parameters that encode our ignorance about…”
Proper motions and dynamics of the Milky Way globular cluster system fromGaiaDR2 (2018, background): “At large galactocentric distances, the distribution becomes radially anisotropic, with the value of anisotropy parameter β ' 0.6 similar to that of the stellar halo (e.g., Deason et al. 2012; Kafle et al. 2014; Belokurov et al. 2018; Wegg et al. 2018, among others).”