The RAVE survey: the Galactic escape speed and the mass of the Milky Way

Abstract

We made new estimates of the Galactic escape speed at various Galactocentric radii using the latest data release of the RAdial Velocity Experiment (RAVE DR4). Compared to previous studies we have a database that is larger by a factor of 10, as well as reliable distance estimates for almost all stars. Our analysis is based on statistical analysis of a rigorously selected sample of 90 highvelocity halo stars from RAVE and a previously published data set. We calibrated and extensively tested our method using a suite of cosmological simulations of the formation of Milky Way-sized galaxies. Our best estimate of the local Galactic escape speed, which we define as the minimum speed required to reach three virial radii R 340 , is 533 +54 −41 km s −1 (90% confidence), with an additional 4% systematic uncertainty, where R 340 is the Galactocentric radius encompassing a mean overdensity of 340 times the critical density for closure in the Universe. From the escape speed we further derived estimates of the mass of the Galaxy using a simple mass model with two options for the mass profile of the dark matter halo: an unaltered and an adiabatically contracted Navarro, Frenk & White (NFW) sphere. If we fix the local circular velocity, the latter profile yields a significantly higher mass than the uncontracted halo, but if we instead use the statistics for halo concentration parameters in large cosmological simulations as a constraint, we find very similar masses for both models. Our best estimate for M 340 , the mass interior to R 340 (dark matter and baryons), is 1.3 +0.4 −0.3 × 10 12 M (corresponds to M 200 = 1.6 +0.5 −0.4 × 10 12 M ). This estimate is in good agreement with recently published, independent mass estimates based on the kinematics of more distant halo stars and the satellite galaxy Leo I.

Milky Way mass constraints from the Galactic satellite gap

“…In this case, the fact that the MW has only three satellites with V max ≥ 30 km s −1 (the two MCs and Sagittarius) requires the virial mass of the MW halo to be M 200 < 1.4 × 10 12 M at 90 per cent confidence; on the other hand, the existence of the two MCs, which have V max ≥ 60 km s −1 , requires M 200 > 1.0 × 10 12 M , also at 90 per cent confidence. This conclusion is consistent with some, but not all, recent measurements of the MW mass (Battaglia et al 2005;Smith et al 2007;Xue et al 2008;Guo et al 2010;Watkins, Evans & An 2010;Busha et al 2011a;González, Kravtsov & Gnedin 2014;Diaz et al 2014;Piffl et al 2014).…”

Using the Milky Way satellites to study interactions between cold dark matter and radiation

“…The maximal circular velocity, Vmax, is selected as a measure for the mass and is determined directly from the simulations (it is derived from the observed stellar line-of-sight velocity dispersions using the assumption that Vmax = √ 3σ , . 2σ CL [Piffl et al 2013] 2σ CL [Xue et al 2008] 10 (www.dirac.ac.uk). This equipment was funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/H008519/1, STFC DiRAC Operations grant ST/K003267/1 and Durham University.…”

“…The most crucial condition is the DM halo mass. Motivated by calculations that attempt to reconstruct the MW mass distribution based on the measured kinematics of the observed satellites and stars (Xue et al 2008;Boylan-Kolchin et al 2013;Piffl et al 2013), we consider DM haloes to be MW-like if their mass is in the range (0.8 − 2.7) × 10 12 M .…”

Planes of satellite galaxies: when exceptions are the rule

“…Fardal et al 2013;Cautun et al 2014a,b;González, Kravtsov & Gnedin 2014;Piffl et al 2014;Veljanoski et al 2014, for a compilation of other measurements and discussions of systematic effects see Courteau et al 2014;Wang et al 2015). This results in 2849 MS-II haloes and in 63 COCO haloes in the required mass range.…”