Interstellar extinction at high Galactic latitudes across the whole dust layer in the Galaxy

By use of various methods we estimate interstellar extinction at high Galactic latitudes across the whole dust layer inthe Galaxy in a variety of photometric lters. First, we compare reddening estimates from the 3D map of Green-2019(i) inside and (ii) around 23 Galactic globular clusters, i.e. where (i) the estimates are obtained from the Pan-STARRSphotometry of the cluster stars and (ii) estimates from the Schlegel-1998 (SFD98) map are used due to the lack of thestars in Pan-STARRS. The estimates (i) turn out to be systematically higher than (ii) by E(B − V ) = 0.04 mag. Thismeans that SFD98 underestimates low reddenings by the value E(B − V ) = 0.04 mag. Second, we estimate extinction fromcomparison of photometric observations and theoretical isochrones for 43 Galactic globular clusters. The lowest extinctionis A V = 0.1 mag. Third, we analyze the spatial variations of the observed colours for an unprecedentedly large and completesample of 101810 clump giants with precise parallaxes and photometry from Gaia DR2 and WISE. This sample is selectedby us in the space cylinder with a radius of 700 pc around the Sun and a height of 3600 pc across the whole Galacticdust layer. Until now, complete samples of stars with precise distances and photometry have not been considered at such alarge distance from the Galactic plane. This explains our unexpected results: the Galactic dust layer appears thicker thanpreviously thought - the extinction continues to increase even at a distance of |Z| > 400 pc from the plane of the Galaxy;the mean extinction across the whole half-layer below or above the Sun is A V = 0.2 mag. Fourth, by use of the 3D reddeningmaps of Gontcharov-2017, Lallement-2019, and Green-2019 we calculate the most probable parameters for a new version ofour 3D model of the dust spatial distribution in a wide Galactic neighbourhoods of the Sun. Comparing with other models,our model provides the most accurate predictions of the observed colours of the above mentioned sample of 101810 clumpgiants. This comparison predicts the median reddening E(B − V ) = 0.06 mag for high latitudes |b| > 50 deg, and the dustcontainer of the Gould Belt provides up to a half of this reddening.