# Modelling the chemistry of star-forming filaments - II. Testing filament characteristics with synthetic observations

## TL;DR

This study uses advanced 3D-MHD simulations with detailed chemistry to assess how well synthetic observations can determine filament properties like mass and width, revealing limitations and ways to improve accuracy.

## Contribution

It introduces a comprehensive approach combining synthetic observations with complex chemical modeling to evaluate the reliability of filament property measurements.

## Key findings

- Filament widths of ~0.1 pc can be accurately measured with line and continuum observations.
- Mass estimates from dust emission are within a few percent of true mass.
- Molecular line observations can significantly overestimate filament mass and width, especially for narrow filaments.

## Abstract

We present synthetic continuum and $^{13}$CO and C$^{18}$O line emission observations of dense and cold filaments. The filaments are dynamically evolved using 3D-MHD simulations that include one of the largest on-the-fly chemical networks used to date, which models the detailed evolution of H$_2$ and CO. We investigate the reliability of observable properties, in particular filament mass and width, under different simulation conditions like magnetic field orientation and cosmic ray ionisation rate. We find that filament widths of $\sim$0.1 pc can be probed with both line and continuum emission observations with a high accuracy (deviations $\leq$ 20%). However, the width of more narrow filaments can be significantly overestimated by up to a factor of a few. Masses obtained via the dust emission are accurate within a few percent whereas the masses inferred from molecular line emission observations deviate from the actual mass by up to a factor of 10 and show large differences for different $J$ transitions. The inaccurate estimate of filament masses and widths of narrow filaments using molecular line observations can be attributed to (i) the non-isothermal state of the filaments, (ii) optical depth effects, and (iii) the subthermally excited state of CO, while inclination effects and opacity correction only influence the obtained masses and widths by less than 50%. Both, mass and width estimates, can be improved by using two isotopes to correct for the optical depth. Since gas and dust temperature generally differ (by up to 25 K), the filaments appear more gravitationally unstable if the (too low) dust temperature is used for the stability analysis.