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Register a new userThe cumulative mass profile of the Milky Way as determined by globular cluster kinematics from Gaia DR2
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We present new mass estimates and cumulative mass profiles (CMPs) with Bayesian credible regions for the Milky Way (MW) Galaxy, given the kinematic data of globular clusters as provided by (1) the $textit{Gaia}$ DR2 collaboration and the HSTPROMO team, and (2) the new catalog in Vasiliev (2019). We use globular clusters beyond 15kpc to estimate the CMP of the MW, assuming a total gravitational potential model $Phi(r) = Phi_{circ}r^{-gamma}$, which approximates an NFW-type potential at large distances when $gamma=0.5$. We compare the resulting CMPs given data sets (1) and (2), and find the results to be nearly identical. The median estimate for the total mass is $M_{200}= 0.70 times 10^{12} M_{odot}$ and the $50%$ Bayesian credible interval is $(0.62, 0.81)times10^{12}M_{odot}$. However, because the Vasiliev catalog contains more complete data at large $r$, the MW total mass is slightly more constrained by these data. In this work, we also supply instructions for how to create a CMP for the MW with Bayesian credible regions, given a model for $M(<r)$ and samples drawn from a posterior distribution. With the CMP, we can report median estimates and $50%$ Bayesian credible regions for the MW mass within any distance (e.g., $M(r=25text{kpc})= 0.26~(0.20, 0.36)times10^{12}M_{odot}$, $M(r=50text{kpc})= 0.37~(0.29, 0.51) times10^{12}M_{odot}$, $M(r=100text{kpc}) = 0.53~(0.41, 0.74) times10^{12}M_{odot}$, etc.), making it easy to compare our results directly to other studies.
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We estimate the mass of the Milky Way (MW) within 21.1 kpc using the kinematics of halo globular clusters (GCs) determined by Gaia. The second Gaia data release (DR2) contained a catalogue of absolute proper motions (PMs) for a set of Galactic GCs and satellite galaxies measured using Gaia DR2 data. We select from the catalogue only halo GCs, identifying a total of 34 GCs spanning $2.0 < r < 21.1$ kpc, and use their 3D kinematics to estimate the anisotropy over this range to be $beta = 0.46^{+0.15}_{-0.19}$, in good agreement, though slightly lower than, a recent estimate for a sample of halo GCs using HST PM measurements further out in the halo. We then use the Gaia kinematics to estimate the mass of the MW inside the outermost GC to be $M(< 21.1 mathrm{kpc}) = 0.21^{+0.04}_{-0.03} 10^{12} mathrm{M_odot}$, which corresponds to a circular velocity of $v_mathrm{circ}(21.1 mathrm{kpc}) = 206^{+19}_{-16}$ km/s. The implied virial mass is $M_mathrm{virial} = 1.28^{+0.97}_{-0.48} 10^{12} mathrm{M_odot}$. The error bars encompass the uncertainties on the anisotropy and on the density profile of the MW dark halo, and the scatter inherent in the mass estimator we use. We get improved estimates when we combine the Gaia and HST samples to provide kinematics for 46 GCs out to 39.5 kpc: $beta = 0.52^{+0.11}_{-0.14}$, $M(< 39.5 mathrm{kpc}) = 0.42^{+0.07}_{-0.06} 10^{12} mathrm{M_odot}$, and $M_mathrm{virial} = 1.54^{+0.75}_{-0.44} 10^{12} mathrm{M_odot}$. We show that these results are robust to potential substructure in the halo GC distribution. While a wide range of MW virial masses have been advocated in the literature, from below $10^{12} mathrm{M_odot}$ to above $2 times 10^{12}mathrm{M_odot}$, these new data imply that an intermediate mass is most likely.
We employ Gaia DR2 proper motions for 151 Milky Way globular clusters from Vasiliev (2019) in tandem with distances and line-of-sight velocities to derive their kinematical properties. To assign clusters to the Milky Way thick disk, bulge, and halo we follow the approach of Posti et al. (2018) who distinguished among different Galactic stellar components using starss orbits. In particular, we use the ratio $L_{z}/e$, the $Z$ projection of the angular momentum to the eccentricity, as population tracer, which we complement with chemical abundances extracted from the literature and Monte-Carlo simulations. We find that 20 globular clusters belong to the bar/bulge of the Milky Way, 35 exhibit disk properties, and 96 are members of the halo. Moreover, we find that halo globular clusters have close to zero rotational velocity with average value $<Theta>$ =1$pm$ 4 km s$^{-1}$. On the other hand, the sample of clusters that belong to the thick disk possesses a significant rotation with average rotational velocity 179 $pm$ 6 km s$^{-1}$. The twenty globular clusters orbiting within the bar/bulge region of the Milky Way galaxy have average rotational velocity of 49 $pm$ 11 km s$^{-1}$.
The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.8^{+6.7}_{-2.7} x 10^{11} Msun based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.
Using Gaia DR2 astrometry, we map the kinematic signature of the Galactic stellar warp out to a distance of 7 kpc from the Sun. Combining Gaia DR2 and 2MASS photometry, we identify, via a probabilistic approach, 599 494 upper main sequence stars and 12 616 068 giants without the need for individual extinction estimates. The spatial distribution of the upper main sequence stars clearly shows segments of the nearest spiral arms. The large-scale kinematics of both the upper main sequence and giant populations show a clear signature of the warp of the Milky Way, apparent as a gradient of 5-6 km/s in the vertical velocities from 8 to 14 kpc in Galactic radius. The presence of the signal in both samples, which have different typical ages, suggests that the warp is a gravitationally induced phenomenon.
Milky Way globular clusters (MW GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-IR images and photometry from the VISTA Variables in the Via Lactea Extended Survey (VVVX) allow us to chart previously unexplored regions. Our long term aim is to complete the census of MW GCs. The immediate goals are to estimate the astrophysical parameters, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities and ages. We use the near-IR VVVX survey database, in combination with Gaia DR2 optical photometry, and with the Two Micron All Sky Survey (2MASS) photometry. We report the detection of a heretofore unknown Galactic Globular Cluster at $RA =$ 14:09:00.0; $DEC=-$65:37:12 (J2000). We calculate a reddening of $E(J-K_s)=(0.3pm 0.03)$ mag and an extinction of $A_{K_s}=(0.15pm 0.01)$ mag for this new GC. Its distance modulus and corresponding distance were measured as $(m-M)=(15.93pm0.03)$ mag and $D=(15.5pm1.0)$ kpc, respectively. We estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding $[Fe/H]=(-0.70pm0.2)$ dex and $t=(11.0pm1.0)$ Gyr. The mean GC PMs from Gaia are $mu_{alpha^ast}=(-4.68 pm 0.47 )$ mas $yr^{-1}$ and $mu_{delta}=(-1.34 pm 0.45)$ mas $yr^{-1}$. The total luminosity of our cluster is estimated to be $M_{Ks}=(-7.76pm 0.5)$ mag. We have found a new low-luminosity, old and metal-rich globular cluster, situated in the far side of the Galactic disk, at $R_{G}=11.2$ kpc from the Galactic centre, and at $z=1.0$ kpc below the plane. Interestingly, the location, metallicity and age of this globular cluster are coincident with the Monoceros Ring (MRi) structure.
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