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.