Milky Way Mass Through Escape Velocity Curve from LAMOST K Giants

Escape velocity has long been used to constrain the mass of the dark matter (DM) halo in the Milky Way (MW). Here, we present a study of the escape velocity curve using a sample of high-velocity K giants with full 6D phase-space information and of relatively good quality, selected from LAMOST DR8 and cross-matched with Gaia DR3. To expand the high-velocity stars to larger distances, we used radius-dependent criteria of total velocity, i.e., v GC > 300 km s −1 for the solar neighborhood and v GC > v min ∼ 0.6 × v esc ( r GC ) for the outer region. We also selected halo stars based on v ϕ − [Fe/H] information to ensure that the sample is isotropic. We modeled the velocity distribution with traditional power-law models to determine the escape velocity in each radial bin. For the first time, we have directly measured a relatively continuous escape velocity curve that can extend to Galactocentric radii of ∼50 kpc, finding a decline in agreement with previous studies. The escape velocity at the solar position yielded by our measurements is 523.7 4 − 13.47 + 12.83 km s − 1 . Combined with the local circular velocity, we estimated the mass of the MW assuming a Navarro–Frenk–White DM profile, which resulted in a total mass of M 200 , total = 0.9 0 − 0.07 + 0.06 × 1 0 12 M ⊙ , with a concentration of c 200 = 13.4 7 − 1.70 + 1.85 . The small uncertainty implies that including the escape velocities beyond the solar neighborhood can result in a more precise mass estimate. Our derived MW mass is consistent with some recent studies using the escape velocity as well as other tracers, which may support a lower mass of the DM halo than in the past.