Upper panel: surface density of stars with extinction corrected magnitude consistent with being red clump stars 5 − 8 kpc from the Sun (specifically 13.5 < μK < 14.5 in Eq. (2)). Several features are notable: (i) the B/P bulge of the Milky Way in the central 10°; (ii) the higher surface density of stars at l > 0 compared to l < 0 outside the bulge near to the Galactic plane, indicative of the extension of the bar outside the bulge; and (iii) the tilt of the Galactic plane towards the edge of the plot at |l|> 70°, which is indicative of the warp/ripples in the outer disc of the Milky Way. We used near-infrared (NIR) data from the VVV1 survey (Smith et al. 2017) where available, falling back to UKIDSS-GPS2 data (Lucas et al. 2008), and finally 2MASS3 (Skrutskie et al. 2006). After combining these three datasets only a few small regions lacked NIR of sufficient depth and these are left white. Lower panel: fraction of stars in the upper panel which have proper motions in Gaia DR2. Outside the ∼1° thick dust layer in the inner Galaxy, almost all possible target RCGs have Gaia proper motions. Our selected fields, shown in red, are located in the bar outside the bulge. We show a zoom of the red dashed region containing our fields in Fig. 2.
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