Atlas and Catalog of Dark Clouds Based on the 2 Micron All Sky Survey

This paper presents an atlas and catalog of dark clouds derived based on the 2 Micron All Sky Survey Point Source Catalog (2MASS PSC). Color excess maps of E(J - H) and E(H - K-S) as well as extinction maps of A(J), A(H), and A(KS) covering all of the sky have been produced at the 1' grid with a changing angular resolution (similar to 1'-12'), depending on the regions in the sky. Maps drawn at the lower 15' grid with a fixed 1 degrees resolution were also derived for various sets of threshold magnitudes in the J, H, and K-S bands to estimate the background star colors and star densities needed to derive the color excess and extinction maps. The maps obtained in this work are presented on various scales in a series of figures that can be used as an atlas of dark clouds for general research purposes. On the basis of the E(J - H) and A(J) maps drawn at the 1' grid, we have carried out a systematic survey for dark clouds all over the sky. In total, we identified 7614 dark clouds, and measured the coordinates, extents, and A(V) values for each of them. We also searched for their counterparts in a previously published catalog of dark clouds based on the optical photographic plates DSS (Dobashi et al. 2005, PASJ, 57, S1). These cloud parameters, including the information of the counterparts, are compiled into a new catalog of dark clouds. The atlas and catalog organized in this paper mainly trace relatively dense regions in dark clouds, revealing a number of dense cloud cores leading to star formation, while those presented by Dobashi et al. based on the optical database are more suited to trace less-dense regions and to reveal the global extents of dark clouds. These two datasets are complementary, and all together, they are useful to picture the structures of dark clouds in various density ranges.