2022MNRAS.511.3863E

We use Gaia photometry and astrometry to estimate the vertical spatial structure of the Milky Way at the Solar radius, formally accounting for sample incompleteness (the selection function) and parallax measurement uncertainty. Our results show impressive precision demonstrating the power of the Gaia data. However, systematic errors dominate the parameter value uncertainties. We thoroughly test and quantify the impacts of all systematic uncertainties. The vertical tracer density is modelled as a sum of two exponential profiles for the thin and thick discs, together with a spherically symmetric power law for the stellar halo. We constrain the thin disc scale height as h_Tn=260 ±3 (stat) ±26 pc (sys) and thick disc h_Tk=693 ±7 (stat) ±121 pc (sys). For the halo, we obtain a power-law profile with n_H=3.543±0.023 (stat) ±0.259 (sys). We infer a local stellar mass density for non-compact object stars of ρ_local^* = 3.66±0.03 (stat)±0.52 ×10^–2 M_☉ pc^–3 (sys) and surface density of Σ_local^* = 23.17±0.08 (stat)±2.43 M_☉pc^–2 (sys). We find asymmetries above and below the disc with longer disc scale heights in the north but a flatter halo in the south at the <= 10 per cent level.