Probing the physics of star formation (ProPStar): III. No evidence of dissipation of turbulence down to 20 mpc (4000 au) scale

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 αk-5/3, while for supersonic turbulence it is αk-2. Aims. We 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 analyzed observations of the nearby NGC 1333 star-forming region in three different tracers to cover the different scales from ~10 pc down to 20 mpc. The largest scales are covered with the low-density gas tracer 13CO (1- 0) obtained with a single dish, the intermediate scales are covered with single-dish observations of the C18O (3- 2) line, while the smallest scales are covered in H13CO+ (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 ± 0.1 and no evidence of dissipation. Moreover, there is evidence that the power spectrum of the ions to have more power at smaller scales than the neutrals, which is opposite to the theoretical expectations. Conclusions. We show new possibilities for studying the dissipation of energy at small scales in star-forming regions provided by interferometric observations.