Core formation via filament fragmentation and the impact of ambient pressure on it

TL;DR

This study investigates how ambient pressure influences the formation and shape of prestellar cores within filaments, revealing different core morphologies and dynamic behaviors under varying pressure conditions.

Contribution

It demonstrates that ambient pressure determines whether prolate or oblate cores form via filament fragmentation and links velocity gradient features to filament evolution mechanisms.

Findings

Low pressure leads to prolate core formation.

Moderate pressure results in oblate cores through Jeans-like fragmentation.

Higher pressure causes fragments to rebound and prevents core survival.

Abstract

Prestellar cores are generally spheroidal, some of which appear oblate while others appear prolate. Very few of them appear circular in projection. Little, however, is understood about the processes or the physical conditions under which prolate/oblate cores form. We find that an initially sub-critical filament experiencing relatively low pressure ($\lesssim 10^{4}$ K cm$^{-3}$) forms prolate cores (i.e., those with axial ratios in excess of unity) via gradual accumulation of gas in density crests. Meanwhile, a filament that is initially transcritical and experiences pressure similar to that in the Solar neighbourhood (between $\mathrm{few}\ \times 10^{4}$ K cm$^{-3}$ - $\mathrm{few}\ \times 10^{5}$ K cm$^{-3}$) forms oblate cores (i.e., those with axial ratios less than unity) via \emph{Jeans like} fragmentation. At higher pressure, however, fragments within the filament do not tend to survive as they rebound soon after formation. We also argue that quasi-oscillatory features of velocity gradient observed along the filament axis, and in the direction orthogonal to the axis, are integral to the filament evolution process and arise due to the growth of corrugations on its surface. The axial component of the velocity gradient, in particular, traces the gas-flow along the filament length. We therefore posit that it could be used to constrain the filament-formation mechanism. The magnitude of the respective components of velocity gradients increases with increasing external pressure.