Shedding light on the Milky Way rotation curve with Gaia DR2

We present the first attempt to apply the relativistic kinematics delivered by Gaia to trace the Milky Way (MW) rotation curves within a general relativistic scenario. In particular; we have tested an axially symmetric, stationary and asymptotically flat Galaxy-scale metric. The mass inside a large portion of the Galaxy, far away from the central bulk, has been simplified as a pressure-less perfect fluid avoiding the bulge where resides the axis of symmetry. 

The study of the rotation curve profile of our Galaxy required the selection of the most suitable stellar tracers of the bulk circular velocity around the galactic center. We selected DR2 sources according to the requirements for a proper 6-dimensional reconstruction of the phase-space location occupied by each individual star as derived by the same observer. The relativistic fit to the MW rotational data has been compared with well-studied classical models for the MW (MWC), which is comprised of a bulge, a stellar thin and thick disk and a Navarro-Frenk-White (NFW) dark matter (DM) halo. To quantitatively asses this comparison, a Monte Carlo Markov Chain (MCMC) analysis has been done.

For the likelihood analysis, the relativistic and the MWC models appear almost identically consistent with the data. Nevertheless, as for the local baryonic matter density estimated via the 00-term of then Einstein field equation, we have obtained a value that is perfectly in line with current independent estimates, which implies no need of extra-mass.