Modelling the Milky Way. I -- Method and first results fitting the thick
  disk and halo with DES-Y3 data
  We present MWFitting, a method to fit the stellar components of the Galaxy by
comparing Hess Diagrams (HDs) from TRILEGAL models to real data. We apply
MWFitting to photometric data from the first three years of the Dark Energy
Survey (DES). After removing regions containing known resolved stellar systems
such as globular clusters, dwarf galaxies, nearby galaxies, the Large
Magellanic Cloud and the Sagittarius Stream, our main sample spans a total area
of $\sim$2,300 deg$^2$ distributed across the DES footprint. We further explore
a smaller subset ($\sim$ 1,300 deg$^2$) that excludes all regions with known
stellar streams and stellar overdensities. Validation tests on synthetic data
possessing similar properties to the DES data show that the method is able to
recover input parameters with a precision better than 3\%. Based on the
best-fit models, we create simulated stellar catalogues covering the whole DES
footprint down to $g = 24$ magnitude. Comparisons of data and simulations
provide evidence for a break in the power law index describing the stellar
density of the Milky Way (MW) halo. Several previously discovered stellar
over-densities are recovered in the residual stellar density map, showing the
reliability of MWFitting in determining the Galactic components. Simulations
made with the best-fitting parameters are a promising way to predict MW star
counts for surveys such as LSST and Euclid.
