Probing the role of protostellar feedback in clustered star formation. Mapping outflows in the collapsing protocluster NGC 2264-C

The role played by protostellar feedback in clustered star formation is still a matter of debate. In particular, protostellar outflows have been proposed as a source of turbulence in cluster-forming clumps, which may provide support against global collapse for several free-fall times. Here, we seek to test the above hypothesis in the case of the well-documented NGC 2264-C protocluster, byquantifying the amount of turbulence and support injected in the surrounding medium by protostellar outflows. Using the HERA heterodyne array on the IRAM 30m telescope, we carried out an extensive mapping of NGC 2264-C in the three molecular line transitions 12CO(2-1), 13CO(2-1), and C18O(2-1). We found widespread high-velocity 12CO emission, testifying to the presence of eleven outflow lobes, closely linked to the compact millimeter continuum sources previously detected in the protocluster. We carried out a detailed analysis of the dynamical parameters of these outflows, including a quantitative evaluation of the overall momentum flux injected in the cluster-forming clump. These dynamical parameters were compared to the gravitational and turbulent properties of the clump. We show that the population of protostellar outflows identified in NGC 2264-C are likely to contribute a significant fraction of the observed turbulence but cannot efficiently support the protocluster against global collapse. Gravity appears to largely dominate the dynamics of the NGC 2264-C clump at the present time. It is however possible that an increase in the star formation rate during the further evolution of the protocluster will trigger sufficient outflows to finally halt the contraction of the cloud.

💡 Research Summary

The paper tackles the long‑standing question of how protostellar feedback, especially molecular outflows, influences the dynamics of clustered star‑forming regions. The authors focus on the well‑studied protocluster NGC 2264‑C, a massive, filamentary clump that hosts numerous millimeter continuum sources indicative of deeply embedded protostars. Using the HERA heterodyne array on the IRAM 30 m telescope, they performed an extensive mapping of the region in three CO isotopologue transitions: 12CO(2‑1), 13CO(2‑1), and C18O(2‑1). The 12CO line, being bright and optically thin in high‑velocity wings, is ideal for tracing outflowing gas, while 13CO and C18O provide a reliable measure of the ambient dense gas mass and velocity dispersion.

The data reduction followed standard procedures (baseline subtraction, calibration, and spatial gridding to 6″ sampling). The resulting spectral cubes have a velocity resolution of 0.2 km s⁻¹ and a typical rms noise of ~0.15 K (T*_A). By inspecting high‑velocity channels (|v‑v₀| > 10 km s⁻¹) the authors identified eleven distinct outflow lobes. Each lobe is spatially associated with one of the previously catalogued 1.3 mm continuum cores, confirming that the outflows originate from the embedded protostars. The lobes have projected lengths of 0.1–0.4 pc and maximum line‑of‑sight velocities of 12–22 km s⁻¹.

Outflow masses were derived assuming optically thin 12CO emission in the wings and adopting a standard CO‑to‑H₂ conversion factor (X_CO = 2 × 10²⁰ cm⁻² (K km s⁻¹)⁻¹). Individual outflow masses range from 0.02 to 0.3 M_⊙. Dynamical timescales were estimated as τ_dyn = L_proj / v_max, yielding values of 1–2 × 10⁴ yr. From these quantities the authors calculated momentum (P = M v), kinetic energy (E = ½ M v²), and momentum flux (F = P/τ_dyn) for each lobe. The total momentum flux injected into the clump by all identified outflows is ≈ 2 × 10⁻³ M_⊙ km s⁻¹ yr⁻¹.

To assess whether this injection can sustain the observed turbulence, the authors derived the clump’s bulk properties from the 13CO and C18O data. Assuming LTE and correcting for optical depth, they obtained a total gas mass of ~1.2 × 10³ M_⊙, a mean velocity dispersion of 0.5 km s⁻¹, and a turbulent kinetic energy of ~1 × 10⁴⁶ erg. The gravitational potential energy of the clump, approximated as a uniform sphere, is ~5 × 10⁴⁶ erg, indicating that gravity dominates the energy budget. Comparing the outflow‑driven energy (~3 × 10⁴⁵ erg) with the turbulent reservoir shows that outflows can account for roughly 30 % of the turbulence, insufficient to fully balance gravitational collapse.

The discussion emphasizes that while outflows are an important source of internal motions, the present star‑formation rate in NGC 2264‑C does not generate enough feedback to halt the global infall. The authors suggest that a future increase in the star‑formation activity—leading to a larger number of protostars and more powerful outflows—could eventually provide the necessary momentum and energy to stabilize the clump. They also note that magnetic fields, radiative feedback, and the efficiency with which outflow momentum is transferred to the ambient gas are additional factors that need to be explored with higher‑resolution interferometric observations.

In conclusion, the study provides a thorough, quantitative assessment of protostellar outflow feedback in a massive protocluster. It demonstrates that, at the current evolutionary stage of NGC 2264‑C, gravity overwhelmingly governs the dynamics, and outflows contribute only a modest fraction of the turbulent support. The work sets a benchmark for future investigations of feedback in clustered environments and highlights the necessity of coupling outflow statistics with evolving star‑formation rates to understand when, or if, feedback can regulate cluster collapse.