Multiple CO outflows in Circinus: The churning of a molecular cloud

We present a millimeter-wave study of a cluster of bipolar CO outflows embe dded in the western end of the Circinus molecular cloud complex, G317-4, th at is traced by very high optical extinction. For an assumed distance of 70 0 pc, the entire Circinus cloud is estimated to have a mass of about 5 x 10 (4) M.. The opaque western portion that was mapped in this study has a mass of about 10(3) M., contains a number of embedded infrared sources and vari ous compact 1.3 mm continuum sources, and has a remarkable filamentary stru cture with numerous cavities that appears to be the fossil remnants of past star formation activity. The most active star-forming region in this part of Circinus is centered around a compact cluster of millimeter continuum so urces associated with IRAS 14564-6254 and IRAS 14563-6301, which lies about 7' to the south. This region contains two known Herbig-Haro objects, HH 76 and HH 77, and a profusion of overlapping high-velocity CO outflow lobes. Among these, we can clearly distinguish the two largest outflows in Circinu s (flows A and B), which appear to originate from the two brightest IRAS so urces. This region also contains at least two other prominent but overlappi ng bipolar CO outflows (flows C and C'), one of which may be associated wit h IRAS 14564-6258. Two compact and relatively low-velocity CO outflows lie at the northern periphery of the Circinus core and are associated with IRAS 14563-6250 (flow E), a source also detected as a 1.3 mm continuum source, and with IRAS 14562-6248 (flow G). A small but prominent reflection nebula associated with the nebulous star vBH 65a and a coaxial Herbig-Haro jet, HH 139, is located at the southeastern edge of this cloud core and illuminate s part of a cavity seen as a low-extinction region. A faint and low-mass CO molecular flow is associated with vBH 65a and HH 139 (flow F). The infrare d source IRAS 14580-6303 drives a small CO flow (flow I). A second, active center of star formation is centered on the source IRAS 14592-6311, on the peculiar Herbig Ae/Be star vBH 65b, about 20' to the southeast of the main cloud core; four HH objects, HH 140 through HH 143, and a compact CO outflo w are located here (flow D). About 5' farther south, IRAS 14596-6320 drives yet another outflow (now H). Thus, the mapped portion of Circinus contains at least 10 CO-emitting molecular outflows. Assuming that star formation h as continued at a steady rate for the last several hundred thousand years, the Circinus cloud is expected to have produced dozens of young stars. Thei r outflows have severely altered the structure and kinematics of this cloud , as evidenced by the multitude of prominent cavities and dust filaments th at outline their boundaries. This level of star formation activity is consi stent with the numerous post-outflow phase Ha emission-line stars that have been found in this region. The Circinus cloud complex is an archetypical c ase where star formation activity may have profoundly affected the structur e of a molecular cloud, producing its strikingly filamentary and cavitated appearance and providing further evidence that star formation may be a self -regulated process.