The Milky Way total mass profile as inferred from GAIA DR2

The Milky Way total mass profile as inferred from GAIA DR2

 Face-on (top) and edge-on (bottom) stellar light projection of a high-resolution simulated Milky Way-mass spiral galaxy at the present day from the Auriga Project (Grand et al. (2017 MNRAS.467,179). Bluer colours indicate younger stars and redder colours older stars.

Over the past few years, there has been a breakthrough in the ability to simulate realistic galaxies and galaxy populations through cosmological hydrodynamical simulations. Some of the main programmes in this area have been conducted using DiRAC facilities.

This kind of simulations not only inform us about the physical processes at work during the formation of galaxies but also allow us also to connect cosmological theory directly to astronomical observations. In this work we use simulations from three of the major cosmological hydrodynamics simulations of recent years, the EAGLE, APOSTLE and AURIGA projects with data from the GAIA satellite which has transformed our view of the Milky Way. We use the simulations to construct a detailed physical model of the Milky Way.

Top: MW Galactic rotation curve (symbols with error bars) as a function of radial distance. The solid red line is the best fitting MW mass model assuming a contracted dark matter NFW halo. The dashed blue line is assuming no contraction. Bottom: the difference between the data and the best fitting contracted halo model. The dashed  blue line is the difference between the NFW and a contracted halo model.

The model galaxy contains 6 baryonic subcomponents: a bulge, a thin and a thick stellar disc, an HI and a molecular gas disc and a circumgalactic medium (CGM), all embedded in a dark matter halo. The simulations have shown that the presence of baryons induces a contraction of the dark matter distribution in the inner regions of the galaxy which we include in our Milky Way model.

We fit our model to the Gaia DR2 Galactic rotation curve and other data and find the best-fit model for the Milky Way. This has a dark matter halo mass, MDM = 0.97 ± 0.20 × 1012 Mo, and concentration before baryon contraction of 9.4 ± 1.3, which lie close to the median halo mass–concentration relation predicted in ΛCDM. We provide values for all the baryonic components of the Milky Way.