Dense gas in the Monoceros OB1 dark cloud and its relationship to star formation.

Abstract

We have conducted a CS survey of the 10 outflows and 30 IRAS sources identified by Margulis (1987) in the Mon OB1 dark cloud to study the relationship between outflows, YSOs, and dense cores in this cloud. We have found that the CS J = 2 → 1 transition traces a large portion of the dense, low-velocity components of the outflows in Mon OB1. We find the mass of this component to be nearly an order of magnitude greater than previous estimates of the outflow "core" component. We detected little CS gas around the quiescent sources in this cloud. CS 2 → 1 temperatures and integrated intensities are 2 to 7 and 2 to 14 times higher, respectively, in the vicinities of IRAS sources associated with outflow activity than about the quiescent sources. This implies CS abundances, temperatures and/or densities are enhanced in regions where outflows impact the ambient cloud. The CS 2 → 1 emission is concentrated in two regions encompassing 6 of the 10 previously identified outflows in this cloud. Four of these six outflows are identifiable in CS. Two, previously identified as monopolar outflows, exhibit bipolar structure in CS. We have detected the CS J = 5 → 4 transition in the vicinity of 4 of the 10 outflows in this cloud, and around none of the quiescent IRAS sources. The CS 5 → 4 emission is extended around two of the outflow sources and has been mapped in these regions. CS J = 7 → 6 emission has been mapped about the brightest outflow source in this cloud. The morphology of the 7 → 6 region suggests it may have been part of the collimating structure for the outflow associated with this sources. The velocity structure and binding energies of the 5 → 4 and 7 → 6 cores suggest the outflows are disrupting these cores. The addition of the low-velocity CS outflow component to previous estimates of outflow energetics implies multiple generations of outflows need not be required to support this cloud against collapse. Our results neither support nor rule out the existence of fossil outflows in this cloud. A full-cloud, unbiased survey is required to search for such outflows.