A closer look at the "characteristic" width of molecular cloud filaments

TL;DR

The paper investigates the claimed characteristic width of molecular cloud filaments, revealing that this narrow width distribution results from measurement methodology and averaging effects, not an intrinsic physical scale.

Contribution

It demonstrates that the observed characteristic filament width is an artifact of analysis methods, challenging previous claims of a universal filament width.

Findings

The narrow width distribution arises from averaging along filament spines.

Width varies significantly from filament ends to centers.

The peak width is linked to measurement parameters, not an intrinsic scale.

Abstract

Filaments in Herschel molecular cloud images are found to exhibit a "characteristic width". This finding is in tension with spatial power spectra of the data, which show no indication of this characteristic scale. We demonstrate that this discrepancy is a result of the methodology adopted for measuring filament widths. First, we perform the previously used analysis technique on artificial scale-free data, and obtain a peaked width distribution of filament-like structures. Next, we repeat the analysis on three Herschel maps and reproduce the narrow distribution of widths found in previous studies $-$ when considering the average width of each filament. However, the distribution of widths measured at all points along a filament spine is broader than the distribution of mean filament widths, indicating that the narrow spread (interpreted as a "characteristic" width) results from averaging. Furthermore, the width is found to vary significantly from one end of a filament to the other. Therefore, the previously identified peak at 0.1 pc cannot be understood as representing the typical width of filaments. We find an alternative explanation by modelling the observed width distribution as a truncated power-law distribution, sampled with uncertainties. The position of the peak is connected to the lower truncation scale and is likely set by the choice of parameters used in measuring filament widths. We conclude that a "characteristic" width of filaments is not supported by the available data.