An analysis of the turbulence in the central region of M 42 through structure functions

Abstract

Here, we analyse the character of the turbulence of the Huygens Region in the Orion Nebula (M 42) using structure functions. We compute the second order structure function of a high resolution velocity map in H$\alpha$ obtained through the {\emph MUSE} instrument. Ours is one of the few works that follows a mathematically sound methodology for calculating the second order structure function of astronomical velocity fields. Because of that our results will be useful for future comparisons with other studies of M 42 or other regions. We first analyse the Probability Distribution Function (PDF) and found it consistent with those resulting from numerical simulations of solenoidal turbulence. After a further analysis of the data, we found two possible separate motions or at least regimes in the region. This is confirmed later through the calculation of several filtered structure functions. We found that the turbulence in the Huygens Region is between the Kolmogorov regime ($S_2\propto\delta r^{2/3}$) and the Burgers regime ($S_2\propto\delta r$). We found that the turbulence in the region consists on two flow regimes that reproduce a generalised Larson's Law, $S_2\sim\delta r^{0.74-0.76}$.