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Small scale turbulence alongside with large scale turbulence in a z~sim 2 star Forming Galaxy with outflowing wind, revealed by Multi-point structure functions

Itzhak Goldman

TL;DR

Problem addressed: whether star formation drives small-scale turbulence in a high-redshift star-forming galaxy with an outflow wind (z ~ 2). Approach: apply multi-point second-order structure functions to residual nebular gas and wind velocity fields to identify a break scale $l_s$ and estimate $σ_s$. Key findings: existence of small-scale turbulence with $l_s ≈ 240–290$ pc and $σ_s ≈ 1.84–1.86$ km s^-1; small-scale turbulence carries more energy than the large-scale component on the same scales, with $t_s ≈ 127–155$ Myr. Significance: demonstrates a coexisting multi-scale turbulence picture in a high-redshift galaxy, linking star-formation-driven feedback to a small-scale cascade while large-scale turbulence reflects past interactions.

Abstract

Recently, Goldman (2024) obtained evidence for a large scale compressible, Burgers turbulence in the ism of a gravitationally lensed, star-forming galaxy at $z = 1.87$, with an outflowing wind. The turbulent timescale on the largest spatial scale has been found to be ~500 Myr . This together with the large spatial scale of~ 6.4 kpc suggest a large scale generating mechanism (such as tidal interaction or merger) that lasted for ~500 Myr. On the other hand, the outflowing wind is much younger and is probably the result of the intense star formation. Therefore, could it be that the star formation drives also turbulence on small scales? In the present work we utilize multi-point second order structure functions to find whether there exists also a small scale turbulence in this galaxy, and if so, try to identify its drivers. We obtained evidence for small scale turbulence whose largest spatial scale ~240 pc for the nebular gas velocity field and ~ 290 pc$ for the outflowing wind velocity field. These values suggest that stellar sub clumps or giant star clusters with an high concentration of young massive stars could be responsible for both the outflow and for the small scale turbulence.

Small scale turbulence alongside with large scale turbulence in a z~sim 2 star Forming Galaxy with outflowing wind, revealed by Multi-point structure functions

TL;DR

Problem addressed: whether star formation drives small-scale turbulence in a high-redshift star-forming galaxy with an outflow wind (z ~ 2). Approach: apply multi-point second-order structure functions to residual nebular gas and wind velocity fields to identify a break scale and estimate . Key findings: existence of small-scale turbulence with pc and km s^-1; small-scale turbulence carries more energy than the large-scale component on the same scales, with Myr. Significance: demonstrates a coexisting multi-scale turbulence picture in a high-redshift galaxy, linking star-formation-driven feedback to a small-scale cascade while large-scale turbulence reflects past interactions.

Abstract

Recently, Goldman (2024) obtained evidence for a large scale compressible, Burgers turbulence in the ism of a gravitationally lensed, star-forming galaxy at , with an outflowing wind. The turbulent timescale on the largest spatial scale has been found to be ~500 Myr . This together with the large spatial scale of~ 6.4 kpc suggest a large scale generating mechanism (such as tidal interaction or merger) that lasted for ~500 Myr. On the other hand, the outflowing wind is much younger and is probably the result of the intense star formation. Therefore, could it be that the star formation drives also turbulence on small scales? In the present work we utilize multi-point second order structure functions to find whether there exists also a small scale turbulence in this galaxy, and if so, try to identify its drivers. We obtained evidence for small scale turbulence whose largest spatial scale ~240 pc for the nebular gas velocity field and ~ 290 pc$ for the outflowing wind velocity field. These values suggest that stellar sub clumps or giant star clusters with an high concentration of young massive stars could be responsible for both the outflow and for the small scale turbulence.
Paper Structure (6 sections, 7 equations, 4 figures)

This paper contains 6 sections, 7 equations, 4 figures.

Table of Contents

  1. introduction
  2. Multi-point second order structure functions
  3. Multi-point structure functions of the nebular gas velocity field.
  4. Multi-point structure functions of the outflowing wind velocity field.
  5. Discussion
  6. summary and conclusions

Figures (4)

  • Figure 1: The residual nebular velocity field, and a continuous fit in units of $km/s$ as function of position along the major axis, in units of $207.5$ pc.
  • Figure 2: Multi-point structure functions of the nebular gas velocity field, in units of $(km/s)^2$ as function of spatial lags along the major axis, in units of $207.5$ pc. Blue curve: 3 point structure function. Orange curve: 4 point structure function. Green curve: 5 point structure. Red curve: 6 point structure function.
  • Figure 3: The residual outflowing wind velocity field, and a continuous fit in units of $km/s$ as function of position along the major axis, in units of $207.5$ pc.
  • Figure 4: Multi-point structure functions of the outflowing wind velocity field, in units of $(km/s)^2$ as function of spatial lags along the major axis, in units of $207.5 pc$. Blue curve: 3 point structure function. Orange curve: 4 point structure function. Green curve: 5 point structure. Red curve: 6 point structure function.