Anisotropic Formation of Magnetized Cores in Turbulent Clouds

TL;DR

This study confirms that magnetized core formation in turbulent molecular clouds is anisotropic and primarily governed by dynamic pressure and thermal sound speed, with core properties aligning with observed data.

Contribution

The paper extends previous simulations to quantify how pre-shock conditions influence core properties, confirming the anisotropic formation model and linking core characteristics to turbulence and thermal pressure.

Findings

Core properties depend mainly on turbulence and thermal pressure, not magnetic field strength.

Median core masses and radii match Bonnor-Ebert predictions based on dynamic pressure.

Cores and filaments form simultaneously, with cores comparable to observed Perseus cloud cores.

Abstract

In giant molecular clouds (GMCs), shocks driven by converging turbulent flows create high-density, strongly-magnetized regions that are locally sheetlike. In previous work, we showed that within these layers, dense filaments and embedded self-gravitating cores form by gathering material along the magnetic field lines. Here, we extend the parameter space of our three-dimensional, turbulent MHD core formation simulations. We confirm the anisotropic core formation model we previously proposed, and quantify the dependence of median core properties on the pre-shock inflow velocity and upstream magnetic field strength. Our results suggest that bound core properties are set by the total dynamic pressure (dominated by large-scale turbulence) and thermal sound speed c_s in GMCs, independent of magnetic field strength. For models with Mach number between 5 and 20, the median core masses and radii are comparable to the critical Bonnor-Ebert mass and radius defined using the dynamic pressure for P_ext. Our results correspond to M_core = 1.2 c_s^4/sqrt(G^3 rho_0 v_0^2) and R_core = 0.34 c_s^2/sqrt(G rho_0 v_0^2) for rho_0 and v_0 the large-scale mean density and velocity. For our parameter range, the median M_core ~ 0.1-1 M_sun, but a very high pressure cloud could have lower characteristic core mass. We find cores and filaments form simultaneously, and filament column densities are a factor ~2 greater than the surrounding cloud when cores first collapse. We also show that cores identified in our simulations have physical properties comparable to those observed in the Perseus cloud. Superthermal cores in our models are generally also magnetically supercritical, suggesting that the same may be true in observed clouds.