TUNA Lunch Talk:

Yoshito Shimajiri


Possible External Triggers of Star Formation in the Orion-A Giant Molecular Cloud

January 15

12:10PM, Room 230, NRAO, Edgemont Road


We present new, wide and deep images in the 1.1 mm continuum and the 12CO (J=1–0) emission toward the northern part of the Orion A Giant Molecular Cloud (Orion-A GMC). The 1.1 mm data were taken with the AzTEC camera mounted on the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in Chile, and the 12CO (J=1–0) data with the 25 beam receiver (BEARS) on the NRO 45 m telescope in the On-The-Fly (OTF) mode. This is the widest 1.7 degree × 2.3 degree corresponding to 12 pc × 17 pc) and the highest sensitivity (∼9 mJy beam−1) 1.1 mm dust-continuum imaging with an effective spatial resolution of ∼ 40 arcsec. The 12CO (J=1–0) image was taken over the northern 1.2 degree × 1.2 degree (corresponding 9 pc × 9 pc) area with a sensitivity of 0.93 K in TMB, a velocity resolution of 1.0 km s−1, and an effective spatial resolution of 21arcsec. With these data, as well as the MSX 8 μm, Spitzer 24 μm and the 2MASS data, we have investigated the detailed structure and kinematics of molecular gas associated with the Orion A GMC and have found evidence for interactions between molecular clouds and the external forces that may trigger star formation. Four types of possible triggers were revealed; 1) Collision of the diffuse gas on the cloud surface, particularly at the eastern side of the OMC-2/3 region, 2) UV compression from OB stars that forms shells and filamentary structures of Photo-Dominated Regions (PDR), 3) UV radiation implosion on the pre-existing dense molecular cloud cores in the western region of Ori-KL, and 4) collision of dense gas with the powerful outflows in the OMC-2/3 and the OMC-4 regions. Our wide-field and high-sensitivity imaging has provided the first comprehensive views of the potential sites of triggered star formation in the Orion A GMC.