On the formation of cores in accreting filaments and the impact of ambient environment on it

TL;DR

This study uses hydrodynamic simulations to examine how ambient external pressure influences the formation, physical properties, and star-forming potential of accreting filaments in different environments.

Contribution

It provides new insights into how external pressure and turbulence affect filament fragmentation, core formation, and their physical characteristics in star-forming regions.

Findings

Filaments fragment into spheroidal cores regardless of line mass.

External pressure influences filament width and susceptibility to instabilities.

Velocity gradients along filaments are oscillatory and related to fragmentation scales.

Abstract

Recent numerical works, including ours, lend credence to the thesis that ambient environment, i.e., external pressure, affects star-forming ability of clouds & filaments. In continuation with our series of papers on the subject we explore this thesis further by developing hydrodynamic simulations of accreting filaments confined by external pressures in the range $10^{4 -7}$ $K\ cm^{-3}$. Our findings are-\textbf{(i)} irrespective of linemass, filaments fragment to yield spheroidal cores. Initially sub-critical filaments in low to intermediate external pressure environments form broad cores which suggests, weakly self-gravitating filaments must fragment via \emph{collect-and-collapse} mode to form broad cores. Transcritical filaments, by contrast, become susceptible to Jeans-type instability and form pinched cores; \textbf{(ii)} ambient environment bears upon physical properties of filaments including their {\small FWHM$_{fil}$}. Only those initially suffused with subsonic turbulence in Solar Neighbourhood-like environs, however, have {\small FWHM$_{fil}$}$\sim$ 0.1 $pc$. In high pressure environs they not only have smaller widths, but become severely eviscerated. On the contrary, filaments suffused with initially supersonic turbulence are typically broader; \textbf{(iii)} quasi-oscillatory nature of velocity gradients is ubiquitous along filament lengths and its magnitude generally increases with increasing pressure. The periodicity of the velocity gradients approximately matches the fragmentation lengthscale of filaments; \textbf{(iv)} oscillatory features of the radial component of the velocity gradient are a unreliable proxy for detecting signatures of accretion onto filaments; \textbf{(v)} filaments at either extreme of external pressure are inefficient at cycling gas into the dense phase which could reconcile the corresponding inefficiency of star-formation in such environments.