On estimating angular momenta of infalling protostellar cores from observations

Abstract

We use numerical simulations of molecular cloud formation in the colliding flow scenario to investigate the reliability of observational estimates of the angular momenta of early-state, low-mass protostellar cores. We show that, with suitable corrections for projection factors, molecular line observations of velocity gradients in NH 3 can be used to provide reasonable estimates of core angular momenta within a factor of two to three, with a few large underestimates due to unfavorable viewing angles. Our results differ from previous investigations which suggested that observations might overestimate true angular momenta by as much as an order of magnitude; the difference is probably due to the much smoother velocity field on small scales in our simulations, which result from allowing turbulence to decay and gravitational infall to dominate. The results emphasize the importance of understanding the nature of "turbulent" velocities, with implications for the formation of protostellar disks during core collapse.

The Specific Angular Momentum Radial Profile in Dense Cores: Improved Initial Conditions for Disk Formation

“…Therefore, if we determine the rotational velocity at a given rotation radius then we can derive the specific angular momentum. A similar analysis was performed by Zhang et al (2018) with numerical simulations, showing that the total specific angular momentum could be estimated. In the case of lines that are not very optically thick, the rotational velocity will correspond to the relative centroid velocity of the line along the line-of-sight (V LSR ) with respect of the core center (Tanner & Arce 2010).…”

The JCMT BISTRO Survey: Alignment between Outflows and Magnetic Fields in Dense Cores/Clumps

“…Chen & Ostriker (2018) compared the distributions of the misalignment between the angular momenta and the magnetic fields in the dense cores formed in their 3D turbulent MHD simulations of converging flows with different degrees of the magnetization and turbulence. Their simulations can be roughly classified into three groups: dominant magnetic field (M5 and B20), dominant 47 We note that in numerical simulations with turbulence, rotation in dense cores could be nonuniform (e.g., Dib et al 2010;Zhang et al 2018;Verliat et al 2020). In this case, the outflow direction may not represent the direction of the net angular momentum of an entire dense core but is related to the angular momentum of the material that has been accreted to form the central star-disk system.…”

Numerical Methods for Simulating Star Formation

“…For instance, Kuffmeier et al (2017) and Kuffmeier et al (2018) presented RAMSES AMR zoom-in calculations from an outer scale of 40 pc down to cell sizes of 2 au to study the effect of the environment on the formation and the evolution of protoplanetary disks. Zhang et al (2018) performed high resolution calculations of the formation and evolution of a starforming core, obtained by running larger scale calculations of molecular cloud formation . They used FLASH with a maximum resolution of 25 AU and were able to cover scales from 256 pc to 25 AU (see Figure 5).…”