ROTATION CURVE OF THE MILKY WAY OUT TO ∼200 kpc

Abstract

The rotation curve (RC) of our Galaxy, the Milky Way, is constructed starting from its very inner regions (few hundred pc) out to a large galactocentric distance of ∼ 200 kpc using kinematical data on a variety of tracer objects moving in the gravitational potential of the Galaxy, without assuming any theoretical models of the visible and dark matter components of the Galaxy. We study the effect on the RC due to the uncertainties in the values of the Galactic Constants (GCs) R 0 and V 0 (these being the sun's distance from and circular rotation speed around the Galactic center, respectively) and the velocity anisotropy parameter β of the halo tracer objects used for deriving the RC at large galactocentric distances. The resulting RC in the disk region is found to depend significantly on the choice of the GCs, while the dominant uncertainty in the RC at large distances beyond the stellar disk comes from the uncertainty in the value of β. In general we find that the mean RC steadily declines at distances beyond ∼ 60 kpc, independently of the value of β. Also, at a given radius, the circular speed is lower for larger values of β (i.e., for more radially biased velocity anisotropy). Considering that the largest possible value of β is unity, which corresponds to stellar orbits being purely radial, our results for the case of β = 1 give a lower limit to the total mass of the Galaxy within ∼ 200 kpc, M (200 kpc) > ∼ (6.8 ± 4.1) × 10 11 M ⊙ , independently of any model of the dark matter halo of the Galaxy.

The Rotation of the Hot Gas Around the Milky Way

“…First, the assumption of constant velocity must break down at some radius. An effort to measure the Galactic rotation curve to 200 kpc using disk and non-disk objects found (Bhattacharjee et al 2014) that f v is flat to 80 kpc, while a measurement from disk stars in the Sloan Digital Sky Survey found (Xue et al 2008) that f v in the disk declines by 15% from v LSR at 10-20 kpc and remains constant from 20-55 kpc (the maximum probed). Thus, the assumption of a constant v r or f v within < r 80 kpc appears to be reasonable, and more than 80% of the cumulative equivalent width comes from within this region ( Figure 5).…”

Evidence for dark matter in the inner Milky Way

“…We start by presenting a new, comprehensive compilation of rotation curve data derived from kinematic tracers of the Galactic potential, which considerably improves on earlier (partial) compilations 30,31 . Optimized to Galactocentric radii R = 3-20 kpc, our database includes gas kinematics (HI terminal velocities 3,4 13 .…”

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

“…In order to express the profile better, we apply a power-law fit and find σ r ∝ r ∼−0.38 with the solar peculiar motion 1 (the red dotted line in the Figure 6) & σ r ∝ r ∼−0.37 with the solar peculiar motion 2 (the black solid line in the Figure 6). The changes in the solar basic data (U, V, W and V lsr ) can affect the velocity distributions and final results (also see Bhattacharjee et al(2014)). …”