We present the new wide-field, high spatial and velocity resolution map of the entire CO distribution of the Orion molecular cloud complex and Eridanus loop. The observations were carried out with the NANTEN 4-m radio telescope in the Las Campanas Observatory. The survey covered 615 square degrees at a 4' grid spacing, and the total molecular mass in the observed area is estimated to be 2.3 × 105 M ☉. More than 50 % of the total mass is concentrated in and around the previously known Orion A and B giant molecular clouds. We found many small clouds with a mass of a few M ☉. They are distributed away from OB stars, and some of them show a ring-shaped structure surrounding OB stars. We also detected cometary-shaped clouds even located at a higher galactic latitude. To reveal an extensive image of dense molecular gas (nH_2 >≈ 104-5 cm-3) of Orion A and B giant molecular clouds, we have also carried out systematic observations in H13CO+ (J = 1--0) based on the C18O (J = 1--0) observations. We found that the C18O molecular column density is a good indicator of star formation.
8th Asian-Pacific Regional Meeting, Volume II
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