3D maps of the local ISM from inversion of individual color excess
  measurements
  Three-dimensional (3D) maps of the Galactic interstellar matter (ISM) are a
potential tool of wide use, however accurate and detailed maps are still
lacking. One of the ways to construct the maps is to invert individual
distance-limited ISM measurements, a method we have here applied to
measurements of stellar color excess in the optical. We have assembled color
excess data together with the associated parallax or photometric distances to
constitute a catalog of ~ 23,000 sightlines for stars within 2.5 kpc. The
photometric data are taken from Stromgren catalogs, the Geneva photometric
database, and the Geneva-Copenhagen survey. We also included extinctions
derived towards open clusters. We applied, to this color excess dataset, an
inversion method based on a regularized Bayesian approach, previously used for
mapping at closer distances. We show the dust spatial distribution resulting
from the inversion by means of planar cuts through the differential opacity 3D
distribution, and by means of 2D maps of the integrated opacity from the Sun up
to various distances. The mapping assigns locations to the nearby dense clouds
and represents their distribution at the spatial resolution that is allowed by
the dataset properties, i.e. of the order of ~10 pc close to the Sun and
increasing to ~100 pc beyond 1 kpc. Biases towards nearby and/or weakly
extincted stars make this dataset particularly appropriate to map the local and
neighboring cavities, and to locate faint, extended nearby clouds, both goals
that are difficult or impossible with other mapping methods. The new maps
reveal a ~1 kpc wide empty region in the third quadrant in the continuation of
the so-called CMa tunnel of the Local Cavity, a cavity that we identify as the
Superbubble GSH238+00+09 detected in radio emission maps and that is found to
be bounded by the Orion and Vela clouds.
