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Unveiling the collision between molecular outflows: observational evidence and hydrodynamic simulations

E. Cohen Arazi, P. F. Velázquez, M. E. Ortega, A. Rodríguez-González, E. Alquicira-Peláez, S. Paron, P. Rivera-Ortiz, A. Esquivel

TL;DR

This work tests whether the distinctive southward, conical CO structure in the EGO G338.92+0.55(b) region results from a collision between two neighboring molecular outflows. Combining high-resolution ALMA CO J=3--2 observations with 3D hydrodynamic simulations and synthetic PPV CO maps, the authors compare multiple collision scenarios to the data. The simulations reveal that an interaction between the blue lobes OC1 and OC2 with an impact parameter $b_j = r_j$ best reproduces the observed morphology and the enhanced velocity dispersion, while a non-interacting case fails to explain the features. A simple geometric model yields a collision probability of about 80% at the observed separation, suggesting outflow–outflow collisions may be a more common driver of turbulence and complex morphology in star-forming regions than previously recognized.

Abstract

We present an unexplored scenario for interpreting the outflows in the EGO G338.92+0.55 (b) region (hereafter, EGO G338). Within this framework, we investigate the hypothesis that the interaction between two outflows is responsible for the observed morphology and kinematics of this astrophysical object. To explore this possibility, we reanalyse the region using observational molecular line data. We base our analysis on maps of moments 0, 1, and 2 of the CO emission associated with the molecular outflows. Additionally, we conduct three-dimensional hydrodynamic simulations to examine the presence or absence of a collision between two jets. From our numerical results, we produce synthetic CO images to facilitate a direct comparison with observations. The findings of this study provide compelling evidence that the observed morphology and kinematics in the EGO G338 region are the result of a likely collision between two molecular outflows.

Unveiling the collision between molecular outflows: observational evidence and hydrodynamic simulations

TL;DR

This work tests whether the distinctive southward, conical CO structure in the EGO G338.92+0.55(b) region results from a collision between two neighboring molecular outflows. Combining high-resolution ALMA CO J=3--2 observations with 3D hydrodynamic simulations and synthetic PPV CO maps, the authors compare multiple collision scenarios to the data. The simulations reveal that an interaction between the blue lobes OC1 and OC2 with an impact parameter best reproduces the observed morphology and the enhanced velocity dispersion, while a non-interacting case fails to explain the features. A simple geometric model yields a collision probability of about 80% at the observed separation, suggesting outflow–outflow collisions may be a more common driver of turbulence and complex morphology in star-forming regions than previously recognized.

Abstract

We present an unexplored scenario for interpreting the outflows in the EGO G338.92+0.55 (b) region (hereafter, EGO G338). Within this framework, we investigate the hypothesis that the interaction between two outflows is responsible for the observed morphology and kinematics of this astrophysical object. To explore this possibility, we reanalyse the region using observational molecular line data. We base our analysis on maps of moments 0, 1, and 2 of the CO emission associated with the molecular outflows. Additionally, we conduct three-dimensional hydrodynamic simulations to examine the presence or absence of a collision between two jets. From our numerical results, we produce synthetic CO images to facilitate a direct comparison with observations. The findings of this study provide compelling evidence that the observed morphology and kinematics in the EGO G338 region are the result of a likely collision between two molecular outflows.

Paper Structure

This paper contains 11 sections, 11 equations, 7 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Presentation of the source
  3. ALMA observations: main results
  4. Numerical simulations
  5. Initial numerical setup
  6. Synthetic CO emission
  7. Numerical results
  8. Discussion
  9. Comparison between observations and numerical simulations
  10. Outflow-outflow interaction probability
  11. Conclusions

Figures (7)

  • Figure 1: $^{12}$CO J=3--2 emission distribution integrated (moment 0) between $-$90 and $-$70 km s$^{-1}$ (blue), and between $-$55 and $+$5 km s$^{-1}$ (red). The systemic velocity of the complex is about $-$64 km s$^{-1}$. The black contour levels are at 5, 8, 12, and 18 mJy beam$^{-1}$. The ALMA continuum emission at 340 GHz is represented in green. The position of the five molecular cores is indicate with the yellow crosses. For more details see ortega2023.
  • Figure 2: $^{12}$CO J=3--2 moment 1 (mean velocities) and moment 2 (velocity dispersion) map in colour scale. Black contours show the ALMA continuum emission at $340$ GHz, with levels of $60$, $100$, $200$ mJy beam$^{-1}$. (a) Moment 1 map, between $0$ and $55$ km s$^{-1}$. (b) Moment 1 map, between $0$ and $-55$ km s$^{-1}$. In the case of moment 1 maps, for simplicity, the systemic velocity of the region was set at v$_{\rm LSR}=0$ km s$^{-1}$. (c) Moment 2 map, between $0$ and $55$ km s$^{-1}$. (d) Moment 2 map, between $0$ and $-55$ km s$^{-1}$.
  • Figure 3: Temporal evolution of the density distribution on the $y'=0$ plane. The logarithmic colour bar gives the density in units of g cm$^{-3}$. Both axes are given in parsecs.
  • Figure 4: Comparison of the $^{12}$CO J=3--2 emission obtained at $t=1600$ yr from all runs. The logarithmic colour bar represents the emission in units of erg cm$^{-2}$ s$^{-1}$ sr$^{-1}$
  • Figure 5: Comparison of the first moment ($\bar{v}$) obtained from all runs. The linear colour bar is the $\bar{v}$ in km s$^{-1}$. Both axes are in pc.
  • ...and 2 more figures