New Panoramic View of 12CO and 1.1 mm Continuum Emission in the Orion A Giant Molecular Cloud. I. Survey Overview and Possible External Triggers of Star Formation

Abstract

Abstract We present new, wide, and deep images in the 1.1 mm continuum and the $^{12}$CO ($J$$=$ 1–0) emission toward the northern part of the Orion A Giant Molecular Cloud (Orion-A GMC). The 1.1 mm data were taken with the AzTEC camera mounted on the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in Chile, and the $^{12}$CO ($J$$=$ 1–0) data were with the 25 beam receiver (BEARS) on the Nobeyama Radio Observatory (NRO) 45 m telescope in the On-The-Fly (OTF) mode. The present AzTEC observations are the widest (1$^\circ\!\!\!.$7 $\times$ 2$^\circ\!\!\!.$3, corresponding to 12 pc $\times$ 17 pc) and the highest-sensitivity ($\sim\ $9 mJy beam$^{-1}$) 1.1 mm dust-continuum imaging of the Orion-A GMC with an effective spatial resolution of $\sim\ $40$”$. The $^{12}$CO ($J$$=$ 1–0) image was taken over the northern 1$^\circ\!\!\!.$2 $\times$ 1$^\circ\!\!\!.$2 (corresponding 9 pc $\times$ 9 pc) area with a sensitivity of 0.93 K in $T_{\rm MB}$, a velocity resolution of 1.0 km s$^{-1}$, and an effective spatial resolution of 21$”$. With these data, together with the MSX 8$\ \mu$m, Spitzer 24$\ \mu$m, 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. Two types of possible triggers were revealed: (1) Collisions of the diffuse gas on the cloud surface, particularly at the eastern side of the OMC-2/3 region, and (2) Irradiation of UV on the pre-existing filaments and dense molecular cloud cores. Our wide-field and high-sensitivity imaging has provided the first comprehensive view of the potential sites of triggered star formation in the Orion-A GMC.