Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc
  Gaia data are revolutionizing our knowledge of the evolutionary history of
the Milky Way. 3D maps of the interstellar dust provide complementary
information and are a tool for a wide range of uses. We aimed at building 3D
maps of the dust in the Local arm and surrounding regions. To do so, Gaia DR2
photometric data were combined with 2MASS measurements to derive extinction
towards stars that possess accurate photometry and relative uncertainties on
DR2 parallaxes smaller than 20\%. We applied to the extinctions a new
hierarchical inversion algorithm adapted to large datasets and to a
inhomogeneous target distribution. Each step associates regularized Bayesian
inversions along radial directions and a subsequent inversion in 3D of their
results. Each inverted distribution serves as a prior for the subsequent step
and the spatial resolution is progressively increased. We present the resulting
3D distribution of the dust in a 6 x 6 x 0.8 kpc3 volume around the Sun. Its
main features are found to be elongated along different directions that vary
from below to above the mid-plane: the outer part of Carina-Sagittarius, mainly
located above the mid-plane, the Local arm/Cygnus Rift around and above the
mid-plane and the fragmented Perseus arm are oriented close to the direction of
circular motion. The long spur (nicknamed the split) that extends between the
Local Arm and Carina-Sagittarius, the compact near side of Carina-Sagittarius
and the Cygnus Rift below the Plane are oriented along l=40 to 55 deg. Dust
density images in vertical planes reveal in some regions a wavy pattern and
show that the solar neighborhood within 500 pc remains atypical by its extent
above and below the Plane. We show several comparisons with the locations of
molecular clouds, HII regions, O stars and masers. The link between the dust
concentration and these tracers is markedly different from one region to the
other.
