Massive molecular outflows

Abstract

Abstract. With the aim of understanding the role of massive outflows in high-mass star formation, we mapped in the 12 CO J = 2 − 1 transition 26 high-mass star-forming regions at very early stages of their evolution. At a spatial resolution of 11 bipolar molecular outflows were found in 21 of them. The other five sources show confusing morphology but strong line wings. This high detection rate of bipolar structure proves that outflows common in low-mass sources are also ubiquitous phenomena in the formation process of massive stars. The flows are large, very massive and energetic, and the data indicate stronger collimation than previously thought. The dynamical timescales of the flows correspond well to the free-fall timescales of the associated cores. Comparing with correlations known for low-mass flows, we find continuity up to the high-mass regime suggesting similar flow-formation scenarios for all masses and luminosities. Accretion rate estimates in the 10 4 L range are around 10 −4 M yr −1 , higher than required for low-mass star formation, but consistent with high-mass star formation scenarios. Additionally, we find a tight correlation between the outflow mass and the core mass over many orders of magnitude. The strong correlation between those two quantities implies that the product of the accretion efficiency facc =Ṁacc/(Mcore/t ff ) and fr (the ratio between jet mass loss rate and accretion rate), which equals the ratio between jet and core mass (faccfr = Mjet/Mcore), is roughly constant for all core masses. This again indicates that the flow-formation processes are similar over a large range of masses. Additionally, we estimate median fr and facc values of approximately 0.2 and 0.01, respectively, which is consistent with current jet-entrainment models. To summarize, the analysis of the bipolar outflow data strongly supports theories which explain massive star formation by scaled up, but otherwise similar physical processes -mainly accretion -to their low-mass counterparts.

Bow shocks in a newly discovered maser source in IRAS 20231+3440

“…An approximate value of the progenitor luminosity can be estimated from the corresponding order of magnitude of the momentum rate. Therefore, by adopting the P -L bol and the P-M core relationship of Beuther et al (2002), we can see that even our highest momentum rate corresponds to a YSO of luminosity of 100 L , at most. This momentum rate calculation assumes that the relative motion between the north driving source and the source driving the south clump is approximately zero.…”

“…Therefore, for any feasible jet length the maximum value of the momentum rate is 1.2×10 −4 M yr −1 km s −1 . According to the outflow parameter correlations in Beuther et al (2002), mechanical force (momentum rate) is correlated both to the bolometric luminosity and mass of the core. An approximate value of the progenitor luminosity can be estimated from the corresponding order of magnitude of the momentum rate.…”

SMA observations of the W3(OH) complex: Dynamical differentiation between W3(H2O) and W3(OH)

“…Therefore, episodic and precessing outflows in the W3(H 2 O) might be related to the presence of a binary system. The lack of an Hii region in W3(H 2 O), the presence of strong dust emission and the derived short outflow timescale of (5.6±0.2)×10 3 yr, compared with other high-mass molecular outflows (e. g., Beuther et al 2002;Wu et al 2004;Zhang et al 2005;Sánchez-Monge et al 2013b), suggest that the W3(H 2 O) could be in an early evolutionary stage of the high-mass star formation process. Spectral infall signatures are seen in W3(H 2 O), and an unusually large spherical mass infall rate of (2.3±0.7)×10 −3 M ⊙ yr −1 is derived.…”

Tracing early evolutionary stages of high-mass star formation with molecular lines

“…The parameter p is derived from continuum maps of MDCs or is set to be 1.5 according to a quasi-static infall theory in the inner part of the object (Shu et al 1987;Beuther et al 2002c, see Table 7). The density and temperature distributions are transferred to RATRAN when modelling the emission lines.…”