[Paper Review] The molecular gas content of the Pipe Nebula I. Direct evidence of outflow-generated turbulence in B59?

A. Duarte-Cabral, A. Chrysostomou+5 more|ORCA Online Research @Cardiff (Cardiff University)|May 18, 2012

Astrophysics and Star Formation Studies49 references17 citations

TL;DR

This study uses JCMT HARP observations of CO isotopologues in the Pipe Nebula's B59 region to demonstrate that protostellar outflows directly inject turbulence into dense molecular gas, increasing line widths from ~0.3 to ~1 km s⁻¹ and raising excitation temperatures by 2–3 K. The results show that outflows provide sufficient turbulent energy to support the clump against collapse at sub-parsec scales, with less than half of outflow energy converted into turbulence, indicating a key role in regulating star formation dynamics in quiescent, low-mass cores.

ABSTRACT

The Pipe Nebula is a molecular cloud hosting the B59 region as its only active star-forming clump. While the particular importance of outflows in active star forming regions is subject of debate, the quiet nature of the gas in B59 makes it a good site to directly see the impact of protostellar feedback on the quiescent dense gas. Using HARP at the JCMT, we mapped the B59 region with the J=3-2 transition of 12CO to study the kinematics and energetics of the outflows, and 13CO and C18O to study the overall dynamics of the ambient cloud, the physical properties of the gas, and the hierarchical structure of the region. The B59 region has a total of 30Msun of cold and quiescent material, mostly gravitationally bound, with narrow line widths throughout. Such low levels of turbulence in non-star-forming sites of B59 are indicative of the intrinsic initial conditions of the cloud. On the other hand, close to the forming protostars the impact of the outflows is observed as a localised increase of both line widths from 0.3 to 1 km/s, and 13CO excitation temperatures by 2-3K. The impact of the outflows is also evident in the low column density material which shows signs of being pushed, shaped and carved by the outflow bow shocks as they pierce their way out of the cloud. Much of this structure is readily apparent in a dendrogram analysis of the cloud. The low mass of B59 together with its intrinsically quiescent gas and small number of protostars, allows the identification of specific regions where the outflows from the embedded sources interact the dense gas. Our study suggests that outflows are an important mechanism for injecting and sustaining supersonic turbulence at sub-parsec size scales. We find that less than half of the outflow energy is deposited as turbulent energy of the gas, however this turbulent energy is sufficient to slow down the collapse of the region.

Motivation & Objective

• To investigate the impact of protostellar outflows on the dynamics and energy budget of the B59 star-forming region in the Pipe Nebula.
• To determine whether outflows are a significant source of turbulence in dense, quiescent molecular gas, particularly in low-mass, low-velocity environments.
• To assess the efficiency of outflow energy deposition into turbulent motions and its role in supporting the cloud against gravitational collapse.
• To compare the detectability of outflow-generated turbulence in quiescent regions like B59 versus more dynamic regions such as Serpens.
• To evaluate the role of initial gas conditions in determining the observability and impact of outflow-driven turbulence.

Proposed method

• Mapped the B59 region in the 12 CO J=3→2, 13 CO J=3→2, and C 18 O J=3→2 transitions using the HARP instrument on the James Clerk Maxwell Telescope (JCMT).
• Used 13 CO and C 18 O line profiles to derive gas temperature, column density, and velocity dispersion, identifying regions of enhanced turbulence.
• Applied dendrogram analysis to decompose the clump’s hierarchical structure and interpret kinematic features in context of outflow activity.
• Quantified outflow energetics by estimating kinetic energy and momentum injection from protostellar sources and compared them to turbulent energy in the surrounding gas.
• Assessed the balance between gravitational potential energy and turbulent kinetic energy to evaluate dynamical support in the core.
• Used GILDAS and Starlink software for data reduction and analysis, with careful attention to beam-averaged line widths and excitation temperature estimates.

Experimental results

Research questions

• RQ1 To what extent do protostellar outflows in B59 generate detectable turbulence in the dense, quiescent gas?
• RQ2 How does the energy from outflows compare to the turbulent and gravitational energy in the B59 core?
• RQ3 Why is outflow-generated turbulence more easily detectable in B59 than in more dynamic regions like Serpens?
• RQ4 What is the efficiency of outflow energy conversion into turbulent motions in low-mass, low-velocity molecular cores?
• RQ5 Does the observed turbulence support the B59 clump against gravitational collapse, and if so, how long-lived is this support?

Key findings

• The B59 region contains approximately 30 M⊙ of cold, quiescent, gravitationally bound gas with narrow line widths (~0.3 km s⁻¹) in non-star-forming zones.
• Near protostars, C 18 O line widths increase from ~0.3 km s⁻¹ to ~1 km s⁻¹, and 13 CO excitation temperatures rise by 2–3 K, indicating localized outflow-driven turbulence.
• Outflows shape low-column-density gas into bow shock-like structures, visible in dendrogram analysis, confirming their role in modifying the cloud's morphology.
• Less than half of the outflow energy is converted into turbulent energy in the immediate vicinity of the outflows, with the remainder deposited outside the core.
• The turbulent energy input is sufficient to support the B59 clump against collapse at sub-parsec scales (~0.1–0.3 pc), as evidenced by comparable kinetic and potential energies.
• Outflow-generated turbulence is only detectable when the initial gas linewidth is low (≤0.4 km s⁻¹), explaining its absence in more turbulent regions like Serpens despite similar linewidths.