A submillimetre survey of the kinematics of the Perseus molecular cloud - II. Molecular outflows

Abstract

We present a census of molecular outflows across four active regions of star formation in the Perseus molecular cloud (NGC 1333, IC348/HH211, L1448 and L1455), totalling an area of over 1000 arcmin 2 . This is one of the largest surveys of outflow evolution in a single molecular cloud published to date. We analyse large-scale, sensitive CO J = 3 → 2 data sets from the James Clerk Maxwell Telescope, including new data towards NGC 1333. Where possible we make use of our complementary 13 CO and C 18 O data to correct for the 12 CO optical depth and measure ambient cloud properties. Of the 65 submillimetre cores in our fields, we detect outflows towards 45. 24 of these are marginal detections where the outflow's shape is unclear or could be confused with the other outflows. We compare various parameters between the outflows from Class 0 and I protostars, including their mass, momentum, energy and momentum flux. Class 0 outflows are longer, faster, more massive and have more energy than Class I outflows. The dynamical time-scales we derive from these outflows are uncorrelated to the age of the outflow driving source, computed from the protostar's bolometric temperature. We confirm the results of Bontemps et al. that outflows decrease in force as they age. There is a decrease in momentum flux from the Class 0 to I stage: F CO = (0.8 ± 0.3) × 10 −4 compared to (1.1 ± 0.3) × 10 −5 M km s −1 yr −1 , suggesting a decline in the mass accretion rate assuming the same entrainment fraction for both classes of outflow. If F rad = L bol /c is the flux expected in radiation from the central source, then F CO (Class I) ∼ 100F rad and F CO (Class 0) ∼ 1000F rad . Furthermore, we confirm there are additional sources of mass loss from protostars. If a core's mass is only lost from outflows at the current rate, cores would endure a few million years, much longer than current estimates for the duration of the protostellar stage. Finally, we note that the total energy contained in outflows in NGC 1333, L1448 and L1455 is greater than the estimated turbulent energy in the respective regions, which may have implications for the regions' evolution.

The link between molecular cloud structure and turbulence

“…This appears to be consistent with the scales observed in low-mass star-forming regions (e.g. as seen in velocity channel maps in NGC 1333, Quillen et al 2005;Curtis et al 2010). However, Cygnus X forms a large number of highmass stars, which are expected to drive more energetic and most likely larger outflows compared to their model.…”

Warm gas in protostellar outflows

“…Therefore, the mass of the warm gas traced by our mid-J CO observations is not significantly different (considering the errors and different calculation methods) with respect to mass inferred with low-J CO transitions. The major discrepancy is with the CO (3−2) estimations of Curtis et al (2010). However, accounting for the opacity effects that these authors took into account, but also the different velocity range of the integrated maps (Curtis et al 2010 considered velocities from 2 km s −1 away from the cloud velocity, while our maps include emission only from ∼5 km s −1 away from the cloud velocity), we found that the results would be similar (in total a factor of ∼3 × 1.3 higher than the value reported without accounting for those effects for the opacity and velocity range).…”

“…However, accounting for the opacity effects that these authors took into account, but also the different velocity range of the integrated maps (Curtis et al 2010 considered velocities from 2 km s −1 away from the cloud velocity, while our maps include emission only from ∼5 km s −1 away from the cloud velocity), we found that the results would be similar (in total a factor of ∼3 × 1.3 higher than the value reported without accounting for those effects for the opacity and velocity range). Similarly, CO (2−1) observations of the IRS3 outflow (Kwon et al 2006) and CO (3−2) observations of the HH211 outflow (Curtis et al 2010) reported mass estimates of 0.003 M and 0.009 M , respectively, which are similar within the errors to our results based on the CO (6−5) emission (see Table 7). A previous study by van Kempen et al (2009a) in the low-mass outflow HH46 has shown the same trend, i.e., that when considering the errors and difference in the mass estimation method, low-J and mid-J CO lines yield similar results in the mass calculations.…”

“…From previous CO (2−1) observations in L1448-mm the total mass was estimated to be 0.056 M using a T ex of about 15 K (Bachiller et al 1990). In addition, measurements from the CO (3−2) line by Curtis et al (2010) yield a total mass of 0.15 M using a T ex of 50 K and correcting for inclination and opacity effects. In our calculation for the outflow gas observed in CO (6−5) we obtained a mass of 0.029 M .…”

Impacts of pure shocks in the BHR71 bipolar outflow

“…This is the case for the outflows in the Perseus cloud (NGC 1333, L1448, HH211, L1455, e.g. Curtis et al 2010;Gomez-Ruiz et al 2013). The conclusion is that either BHR71 is indeed more energetic than its low-mass counterparts, or that our method partly based on shock modelling naturally yields higher numbers than in all these studies, that often make use of fewer CO lines, for instance, than in the present work.…”