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We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the Milky Way using the scale-free mass estimator of Watkins et al. (2010). We first determine the anisotropy parameter β , and the tracer satellites' radial density index γ to be β  = |$-0.67^{+0.45}_{-0.62}$| and γ = 2.11 ± 0.23. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to β  = |$-0.21^{+0.37}_{-0.51}$|⁠. We find that the index of the Milky Way's gravitational potential α , which is dependent on the mass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on the mass estimator. We found that the mass estimator is biased when applied naively to the satellites of simulated Milky Way haloes. Correcting for this bias, we obtain for our Galaxy a mass of |$0.58^{+0.15}_{-0.14}\times 10^{12}$|  M⊙ within 64 kpc, as computed from the inner half of our observational sample, and |$1.43^{+0.35}_{-0.32}\times 10^{12}$|  M⊙ within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of |$M_\mathrm{vir\, \Delta =97}=1.51^{+0.45}_{-0.40} \times 10^{12}\,{\rm M}_{\odot }$| corresponding to a virial radius of R vir = 308 ± 29 kpc. This value of the Milky Way mass lies in-between other mass estimates reported in the literature, from various different methods. [ABSTRACT FROM AUTHOR]

The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime (⁠|$ \rm [Fe/H] \lt -3$|⁠), and currently consists of over 4 million FGK-type stars over a sky area of |$\sim 2500\, \mathrm{deg}^2$|⁠. We focus our analysis on a subsample of ∼80 000 main-sequence turn-off stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at |$ \rm [Fe/H] =-1.6$|⁠ , and a slope of Δ(LogN)/ |$\Delta \rm [Fe/H] = 1.0 \pm 0.1$| in the metallicity range of |$-3.4\; \lt\; \rm [Fe/H]\; \lt -2.5$|⁠. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low-latitude field in the anticentre direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4 for |$ \rm [Fe/H]\; \lt\; -2.5$| and 1.5 for |$ \rm [Fe/H]\; \lt\; -3$|⁠ , suggesting that the lack of low-metallicity globular clusters in the Milky Way is not due simply to statistical undersampling. [ABSTRACT FROM AUTHOR]