Probing the Physics of Star-Formation (ProPStar) III. No evidence for dissipation of turbulence down to 20 mpc (4 000 au) scale

TL;DR

This study analyzes the turbulence power spectrum in a star-forming molecular cloud across scales from 10 parsecs to 20 milliparsecs, finding no evidence of turbulence dissipation down to the smallest scales observed.

Contribution

It provides the first detailed power spectrum analysis over two decades of spatial scales in an active star-forming region, with no signs of turbulence dissipation at small scales.

Findings

Power spectrum follows a single power-law with an exponent of 2.9±0.1.

No evidence of turbulence dissipation down to 20 mpc scale.

Ion power spectrum shows more power at small scales than neutrals, contrary to expectations.

Abstract

Context. Turbulence is a key component of molecular cloud structure. It is usually described by a cascade of energy down to the dissipation scale. The power spectrum for subsonic incompressible turbulence is $k^{-5/3}$, while for supersonic turbulence it is $k^{-2}$. Aims. We aim to determine the power spectrum in an actively star-forming molecular cloud, from parsec scales down to the expected magnetohydrodynamic (MHD) wave cutoff (dissipation scale). Methods. We analyze observations of the nearby NGC 1333 star-forming region in three different tracers to cover the different scales from $\sim$10 pc down to 20 mpc. The largest scales are covered with the low density gas tracer $^{13}$CO (1-0) obtained with single dish, the intermediate scales are covered with single-dish observations of the C$^{18}$O (3-2) line, while the smallest scales are covered in H$^{13}$CO$^+$ (1-0) and HNC (1-0) with a combination of NOEMA interferometer and IRAM 30m single dish observations. The complementarity of these observations enables us to generate a combined power spectrum covering more than two orders of magnitude in spatial scale. Results. We derive the power spectrum in an active star-forming region spanning more than 2 decades of spatial scales. The power spectrum of the intensity maps shows a single power-law behavior, with an exponent of 2.9$\pm$0.1 and no evidence of dissipation. Moreover, there is evidence for the power-spectrum of the ions to have more power at smaller scales than the neutrals, which is opposite from theoretical expectations. Conclusions. We show new possibilities of studying the dissipation of energy at small scales in star-forming regions provided by interferometric observations.