A study of high velocity molecular outflows with an up-to-date sample

Abstract

Abstract.A statistical study of the properties of molecular outflows is performed based on an up-to-date sample. 391 outflows were identified in published articles or preprints before February 28, 2003. The parameters of position, morphology, mass, energy, outflow dynamics and central source luminosity are presented for each outflow source. Outflow lobe polarity is known for all the sources, and 84% are found to be bipolar. The sources are divided into low mass and high mass groups according to either the available bolometric luminosity of the central source or the outflow mass. The pace of discovery of outflows over the past seven years has increased much more rapidly than in previous periods. Surveys for outflows are still continuing. The number of high-mass outflows detected (139) has considerably increased, showing that they are commonly associated with massive as well as low mass stars. Energetic mass ejection may be a common aspect of the formation of high mass as well as low mass stars. Outflow masses are correlated strongly with bolometric luminosity of the center sources, which was obtained for the first time. There are also correlations between the central source luminosity and the parameters of mechanical luminosity and the thrust or force necessary to drive the outflow. The results show that flow mass, momentum and energy depend on the nature of the central source. Despite their similarity, there are differences between the high mass and low mass outflows. Low mass outflows are more collimated than high mass outflows. On average, the mass of high mass sources can be more than two orders of magnitude larger than those of low mass outflows. The relation between flow mass and dynamical time appears to differ for the two types of outflows. Low mass sources make up 90% of outflows associated with HH objects while high mass outflows make up 61% of the sources associated with H 2 O masers. Sources with characteristics of collapse or infall comprise 12% of the entire outflow sample. The spatial distribution of the outflow sources in the Galaxy is presented and the local occurrence rate is compared with the stellar birth 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.…”

“…For high-mass stars, their formation process is still not well understood. Outflows are frequently detected in high-mass star forming regions, but it is thought that high-mass star formation is not merely a scaled-up version of the low-mass star formation process characterized by larger outflow parameters (e. g., Wu et al 2004), poor collimation around massive young stars (e. g., Shepherd & Churchwell 1996;Zhang et al 2005) and higher accretion rates (see review by Zinnecker & Yorke 2007). Additionally, disks in high-mass young stellar objects are still elusive -only a few of them have been detected (Zhang ⋆ E-mail: slqin@bao.ac.cn Shepherd, Claussen & Kurtz 2001;Patel et al 2005;Jiang et al 2005;Sánchez-Monge et al 2013a -probably due to their short lifetimes, the necessity of achieving high angular resolution (not available in the observations prior to ALMA) and source confusion in dense clusters.…”

Disk Dispersal: Theoretical Understanding and Observational Constraints

“…In many cases, but not all, these jets are seen together with generally much less collimated molecular outflows (Bally et al 1983). Figure 3 is based on the compilation of literature data of CO-outflows by Wu et al (2004), and shows the relation of the mass loss rate, as determined from CO-line mapping, and the bolometric luminosity of the driving sources, over seven orders of magnitude, and obtained from their infrared SEDs. The plot exhibits a large scatter that is due to the heterogeneity of the sample.…”

Observations of Winds, Jets, and Turbulence Generation in GMCs

“…The statistical properties of about 400 molecular outflows were reviewed by Wu et al(2004) and Wu et al(2005). They found the following correlations: The outflow force (momentum injection rate) scales as logṖ = (−4.92 ± 0.15) + (0.65 ± 0.043)log L bol with a correlation coefficient of 0.72 where L bol is the bolometric luminosity of the source in Solar units andṖ is in units of M km s −1 yr −1 .…”

“…Observations of YSOs reveal evolutionary trends (Reipurth & Bally 1991;Wu et al 2004Wu et al , 2005Wang et al 2005). The youngest, most embedded protostars (Class 0 or young Class I objects) drive slower (10 to 100 km s −1 ) flows predominantly traced by CO, SiO, and shocked H 2 .…”