# Dynamical origin of non-thermal states in galactic filaments

## TL;DR

This study uses numerical simulations of self-gravitating particles to demonstrate that galactic filaments naturally evolve into non-thermal steady states with density profiles and temperature inversions similar to observations, indicating a dynamical origin.

## Contribution

It introduces a comprehensive numerical analysis showing that non-thermal states in galactic filaments can arise dynamically from gravitational collapse and perturbations, linking simulations to observed features.

## Key findings

- Non-thermal steady states match observed filament profiles.
- Temperature inversion occurs in cold collapse scenarios.
- Non-thermal states may be common in systems with long-range interactions.

## Abstract

Observations strongly suggest that filaments in galactic molecular clouds are in a non-thermal state. As a simple model of a filament we study a two-dimensional system of self-gravitating point particles by means of numerical simulations of the dynamics, with various methods: direct $N$-body integration of the equations of motion, particle-in-cell simulations and a recently developed numerical scheme that includes multiparticle collisions in a particle-in-cell approach. Studying the collapse of Gaussian overdensities we find that after the damping of virial oscillations the system settles in a non-thermal steady state whose radial density profile is similar to the observed ones, thus suggesting a dynamical origin of the non-thermal states observed in real filaments. Moreover, for sufficiently cold collapses the density profiles are anticorrelated with the kinetic temperature, i.e., exhibit temperature inversion, again a feature that has been found in some observations of filaments. The same happens in the state reached after a strong perturbation of an initially isothermal cylinder. Finally, we discuss our results in the light of recent findings in other contexts (including non-astrophysical ones) and argue that the same kind of non-thermal states may be observed in any physical system with long-range interactions.