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 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, that is, $v_{ \rm GC}>300\;\rm{ km s^{ -1}}$ for the solar neighborhood; $v_{ \rm GC}>v_{ \rm min}\sim0.6\times v_{ \rm esc}(r_{ \rm GC})$ for outer region. We also selected halo stars based on $v_{ \phi}-{ \rm [Fe/H]}$ 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 $\sim 50$ kpc, finding a decline in agreement with previous studies. The escape velocity at the solar position yielded by our measurements is $523.74^{ +12.83}_{ -13.47}\;\rm{ km s^{ -1}}$. 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 $M_{ 200,\;\rm{ total}}=0.90_{ -0.07}^{ +0.06}\times 10^{ 12}\;M_{ \odot}$, with a concentration of $c_{ 200}=13.47_{ -1.70}^{ +1.85}$. 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.
Categories: astro-ph.GA