Broken degeneracies: the rotation curve and velocity anisotropy of the Milky Way halo

Deason, Alis J.; Belokurov, V.; Evans, N. W.; An, J.

doi:10.1111/j.1745-3933.2012.01283.x

Cited by 138 publications

(194 citation statements)

References 44 publications

(77 reference statements)

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“…Solar neighborhood measurements, using full 3D velocity information, find a radially biased β, shown in red Bond et al 2010). The remaining error bars show estimates of β for distant (D10 kpc) halo stars using LOS velocity distributions (Sirko et al 2004;Deason et al 2012;Kafle et al 2012;King et al 2015).…”

Section: A Galactic Shellmentioning

confidence: 99%

Isotropic at the Break? 3d Kinematics of Milky Way Halo Stars in the Foreground of M31

Cunningham

Deason

Guhathakurta

et al. 2016

ApJ

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We present the line-of-sight (LOS) velocities for 13 distant main sequence Milky Way halo stars with published proper motions (PMs). The PMs were measured using long baseline (5-7 years) multi-epoch Hubble Space Telescope/Advanced Camera for Surveys photometry, and the LOS velocities were extracted from deep (5-6 hr integrations) Keck II/DEIMOS spectra. We estimate the parameters of the velocity ellipsoid of the stellar halo using a Markov chain Monte Carlo ensembler sampler method. The velocity second moments in the directions of the Galactic (l, b, LOS) coordinate system are v 138 We use these ellipsoid parameters to constrain the velocity anisotropy of the stellar halo. Ours is the first measurement of the anisotropy parameter β using 3D kinematics outside of the solar neighborhood. We find 0.3 0.9 0.4 b = --+ , consistent with isotropy and lower than solar neighborhood β measurements by 2σ (β SN ∼0.5-0.7). We identify two stars in our sample that are likely members of the known TriAnd substructure, and excluding these objects from our sample increases our estimate of the anisotropy to 0.1 1.0which is still lower than solar neighborhood measurements by 1σ. The potential decrease in β with Galactocentric radius is inconsistent with theoretical predictions, though consistent with recent observational studies, and may indicate the presence of large, shell-type structure (or structures) at r∼25 kpc. The methods described in this paper will be applied to a much larger sample of stars with 3D kinematics observed through the ongoing HALO7D program.

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Section: A Galactic Shellmentioning

confidence: 99%

Isotropic at the Break? 3d Kinematics of Milky Way Halo Stars in the Foreground of M31

Cunningham

Deason

Guhathakurta

et al. 2016

ApJ

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“…For regions beyond the Galactic disc, the RC needs to be measured using halo stars, such as the blue horizontal branch (BHB) stars (Xue et al 2008;Deason et al 2012;Kafle et al 2012;Williams & Evans 2015) and the K giants (Bhattacharjee, Chaudhury, & Kundu 2014, hereafter BCK14), globular clusters or dwarf galaxies. For those tracers of halo populations (assuming isotropically distributed), the radial velocity dispersion σr, number density ν and velocity anisotropy parameter β ≡ 1 − σ 2 t /σ 2 r , are linked to the circular velocity Vc through the Jeans equation (see, e.g.…”

mentioning

confidence: 99%

“…Only more recently, some constraints on the anisotropy parameter, mainly for the inner halo ( 25 kpc), have become available, based on some direct/indirect measurements (e.g. Deason et al 2012; Kafle et al 2012; Deason et al 2013).…”

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confidence: 99%

The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution

Huang

Liu

Yuan

et al. 2016

Mon. Not. R. Astron. Soc.

160

179

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The rotation curve (RC) of the Milky Way out to ∼ 100 kpc has been constructed using ∼ 16, 000 primary red clump giants (PRCGs) in the outer disk selected from the LSS-GAC and the SDSS-III/APOGEE survey, combined with ∼ 5700 halo K giants (HKGs) selected from the SDSS/SEGUE survey. To derive the RC, the PRCG sample of the warm disc population and the HKG sample of halo stellar population are respectively analyzed using a kinematical model allowing for the asymmetric drift corrections and re-analyzed using the spherical Jeans equation along with measurements of the anisotropic parameter β currently available. The typical uncertainties of RC derived from the PRCG and HKG samples are respectively 5-7 km s −1 and several tens km s −1 . We determine a circular velocity at the solar position, V c (R 0 ) = 240 ± 6 km s −1 and an azimuthal peculiar speed of the Sun, V ⊙ = 12.1 ± 7.6 km s −1 , both in good agreement with the previous determinations. The newly constructed RC has a generally flat value of 240 km s −1 within a Galactocentric distance r of 25 kpc and then decreases steadily to 150 km s −1 at r ∼ 100 kpc. On top of this overall trend, the RC exhibits two prominent localized dips, one at r ∼ 11 kpc and another at r ∼ 19 kpc. From the newly constructed RC, combined with other constraints, we have built a parametrized mass model for the Galaxy, yielding a virial mass of the Milky Way's dark matter halo of 0.90 +0.07 −0.08 × 10 12 M ⊙ and a local dark matter density, ρ ⊙,dm = 0.32 +0.02 −0.02 GeV cm −3 .

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“…Interestingly, the results of Smith et al(2007) perfect match with our result based on β = 0. Recently, Deason et al(2012) find M (50kpc) =∼ 4.0 × 10 11 M from about 4000 blue horizontal branch stars with the same method as Xue et al(2008) and this paper.…”

Section: Mass Estimatementioning

confidence: 95%

“…Xue et al(2008) present the circular velocity curve and mass of the Galaxy at ∼ 60 kpc by using radial velocity dispersion of 2041 blue horizontal branch (BHB) stars selected from SDSS DR6 and the Jeans equation with two constants of β (β = 0 and 0.37). Jeans equation and analytical models of the phase-space distribution function of the tracer population have been adopted for the circular velocity curve and mass estimate of the Milky Way at different distances (Gnedin et al 2010;Deason et al 2012;Kafle et al 2012). Bhattacharjee et al (2014) consider three different prescriptions of β, one of them has a radially varying β given by β(r) = (1 + r a 2 /r 2 ) −1 (see Binney & Tremaine 2008), where r a is the anisotropy radius.…”

Section: Introductionmentioning

confidence: 99%

The Milky Way's Circular Velocity Curve and Its Constraint on the Galactic Mass with RR Lyrae Stars

Ablimit

Zhao

2017

ApJ

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We present a sample of 1148 ab-type RR Lyrae (RRLab) variables identified from Catalina Surveys Data Release 1, combined with SDSS DR8 and LAMOST DR4 spectral data. We firstly use a large sample of 860 Galactic halo RRLab stars and derive the circular velocity distributions for the stellar halo. With the precise distances and carefully determined radial velocities (the center-of-mass radial velocities) by considering the pulsation of the RRLab stars in our sample, we can obtain a reliable and comparable stellar halo circular velocity curve. We take two different prescriptions for the velocity anisotropy parameter β in the Jeans equation to study the circular velocity curve and mass profile. We test two different solar peculiar motions in our calculation. Our best result with the adopted solar peculiar motion 1 of (U, V, W) = (11.1, 12, 7.2) km s −1 is that the enclosed mass of the Milky Way within 50 kpc is (3.75 ± 1.33) × 10 11 M based on β = 0 and the circular velocity 180 ± 31.92 (km s −1 ) at 50 kpc. This result is consistent with dynamical model results, and it is also comparable to the previous similar works.

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Broken degeneracies: the rotation curve and velocity anisotropy of the Milky Way halo

Cited by 138 publications

References 44 publications

Isotropic at the Break? 3d Kinematics of Milky Way Halo Stars in the Foreground of M31

Isotropic at the Break? 3d Kinematics of Milky Way Halo Stars in the Foreground of M31

The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution

The Milky Way's Circular Velocity Curve and Its Constraint on the Galactic Mass with RR Lyrae Stars

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