2021MNRAS.502.4194G

A statistical method is employed in tandem with new VISTA Variables in the Via Lactea (VVV) near-infrared observations to determine the Sun's distance from the Galactic Centre (r₀, GC), the Sun's height from the local mid-plane (z₀), and to likewise infer the shape of the Galactic ∼10 Gyr old bulge. Specifically, the conclusions stem from an investigation of 715 high-latitude (|b| > 1°) and centrally symmetric concentrated Type II Cepheids (T2Cs) recently identified in the VVV survey by Braga et al. The analysis yields r₀ = 8.35 ± 0.10 kpc and z₀ = 10 ± 2 pc. The T2Cs distribution within the effective bulge radius r_bulge = 2-3 kpc is an ellipsoid exhibiting axial ratios of ≃1:0.7:0.6, with the major axis inclined at an angle θ ≃ -3° to the Sun-GC sightline. T2Cs do not trace a prominent barred structure at distances >1 kpc from the GC. A key conclusion is that analyses of independent optical and infrared Optical Gravitational Lensing Experiment (OGLE) and VVV observations yield consistent results (e.g. r₀ > 8.0 kpc and both observations display a comparable shape of an ellipsoid), thus providing a constrained and reduced systematic uncertainty.