A Single Distance Sample of Molecular Outflows from High-Mass Young Stellar Objects

μm M L et al. km s−1 TA* Tex CO CO CO ◦ ×H2 MJ Mcl Mcr LCO FCO Lbol bipolar molecular outflows molecular outflows Mcore document A Single Distance Sample of Molecular Outflows from High-Mass Young Stellar Objects Naomi A. Ridge12 Toby J.T. Moore1 N.A. Ridge Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, United Kingdom. [email protected] Received / Accepted Single Distance Sample of Outflows Ridge & Moore We have made 2–1 and 1–0 maps of eleven molecular outflows associated with intermediate to highmass young stellar objects (YSOs) in order to establish whether the correlations between outflow parameters and source bolometric luminosity hold in the high-mass regime. It is important to consider the effects of Malmquist-type biases when looking at high-mass YSOs, as they are generally much more distant than their low mass counterparts. We therefore chose only objects located at∼2 kpc.Wefindthattherelationsshowmuchmorescatterthan massY SOs.Wealsofindthatthemass−spectrumissignificantlysteeperinhigh−massoutflows, indicatingalargermass− fractionatlowervelocities, alowcollimationfactor(∼ 1–2) and no Hubble-like relationship. Stars: formation, Stars: winds, outflows, ISM: jets and outflows, ISM: molecules Introduction It has been well established that outflows represent an important evolutionary stage in the formation of low-mass stars bach96, but systematic studies to identify bipolar outflows from massive YSOs have only begun much more recently. There is now growing evidence that bipolar molecular outflows are ubiquitous with YSOs of all masses. Shepherd & Churchwell *sc96a searched for high velocity (HV) CO wings toward ∼ 120 high-mass star forming regions, and found that HV gas was present in ∼ 90% of sources, indicating that molecular outflows are also a common property of high-mass YSOs. Most luminous YSOs seem to have outflows with much wider opening angles than their low-mass counterparts (Richer et al. 2000), but this may be due to the poor resolution that the known flows have been observed with, and/or the poor statistics available due to the small number of flows which have been studied. It is difficult to make predictions about the general properties of high-mass flows due to the selection effects inherent in the small existing samples. Shepherd & Churchwell (1996b) determined the energetics of 5 massive YSO outflows and showed that they fit well onto the correlation between outflow force (, sometimes referred to as momentum flux) and bolometric luminosity presented by e.g. Cabrit & Bertout (1992; hereafter CB)cb92. Henning et al. *henning00 studied three more massive outflows with similar results. However, we have shown (Moore & Ridge, in preparation) that these correlations, which use heterogeneous, unconstrained samples, may be contaminated by biases due to source distance. We have therefore undertaken a program of observations to study a larger sample of high-mass outflows at a single distance of 2 kpc, withconsistentsensitivity, spatialresolutionandanalysis.Thesampleisdiscu The Sample sectionsample We selected a base sample of 25 objects from the compilation of Wu et al. *wu96, with the selection criteria≥ 10, and distance 2.0±0.3 kpc.Thisfullsamplewasreducedtoafinallistof11targetsbyrejectingobjectsknowntohavevery on, forwhichitisdifficulttodefinetheflowextent).T ablesdsampleliststheselectedoutflows.Alloftheseflowshavebeenprevio Refs Observations and Data Analysis obs Observations were carried out between 1998 August and 1999 June at the 15m James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii and at the NRAO 12m Radio Telescope (NRAO) at Kitt Peak, Arizona. JCMT Observations We obtained J=2→1 “flexibly-scheduled” observations between 1998 August and 1999 May and 4 scheduled nights of observations in 1999 July. At the observing frequency of 230GHzthehalf− powerbeamwidthofthetelescopeis21”.WeusedtheDASspectrometerwith1657channels, providinganeffectivevelocityresolut The observations were carried out in raster-mapping mode with a grid spacing of 10′′ producing fully sampled maps. In this mode, the telescope observes one “off” position per row of on-source observations. Maps were repeated 4 times to obtain the required rms sensitivity of 0.2Kper1 resolutionelement.Thereferencepositionswer switchedobservations.