The width of Herschel filaments varies with distance

Abstract

Context. Filamentary structures in nearby molecular clouds have been found to exhibit a characteristic width of 0.1 pc, as observed in dust emission. Understanding the origin of this universal width has become a topic of central importance in the study of molecular cloud structure and the early stages of star formation. Aims. We investigate how the recovered widths of filaments depend on the distance from the observer by using previously published results from the Herschel Gould Belt Survey. Methods. We obtained updated estimates on the distances to nearby molecular clouds observed with Herschel by using recent results based on 3D dust extinction mapping and Gaia. We examined the widths of filaments from individual clouds separately, as opposed to treating them as a single population. We used these per-cloud filament widths to search for signs of variation amongst the clouds of the previously published study. Results. We find a significant dependence of the mean per-cloud filament width with distance. The distribution of mean filament widths for nearby clouds is incompatible with that of farther away clouds. The mean per-cloud widths scale with distance approximately as 4−5 times the beam size. We examine the effects of resolution by performing a convergence study of a filament profile in the Herschel image of the Taurus Molecular Cloud. We find that resolution can severely affect the shapes of radial profiles over the observed range of distances. Conclusions. We conclude that the data are inconsistent with 0.1 pc being the universal characteristic width of filaments.

Filamentary structures of ionized gas in Cygnus X

“…Although the filament-like structure is observed to have a characteristic width that is significantly larger than our spatial resolution, Panopoulou et al (2022) and references therein showed how this may be an artifact due to extended and confusing emission and a fractal like nature of the emission. Using FIR Herschel continuum images, Panopoulou et al (2022) found filaments observed in the Herschel Gould Belt Survey to have a characteristic width of about four times the resolving beam; thus more distant sources appear to have larger widths, but this is apparently resolved to smaller scales in more nearby sources.…”

The widths of magnetised filaments in molecular clouds

“…For supercritial values of B ⊥ , the fwhm Σ distributions presented in Figure 3 all have peaks in the range ∼ 0.03 pc to ∼ 0.05 pc, somewhat below the peak at ∼ 0.1 pc derived by Arzoumanian et al (2011Arzoumanian et al ( , 2019. However, the peak at ∼ 0.1 pc has recently been questioned by Panopoulou et al (2022), based on updated distances to molecular clouds obtained using Gaia data. Panopoulou et al (2022) find that the estimated average filament fwhm Σ in a molecular cloud increases with distance.…”

“…However, the peak at ∼ 0.1 pc has recently been questioned by Panopoulou et al (2022), based on updated distances to molecular clouds obtained using Gaia data. Panopoulou et al (2022) find that the estimated average filament fwhm Σ in a molecular cloud increases with distance. This strongly suggests that unappreciated resolution effects have been overlooked.…”

Dependence of Molecular Cloud Samples on Angular Resolution, Sensitivity, and Algorithms

“…Missing one dimension of position, PPV data are incomplete compared with position-position-position (PPP) data and are unable to distinguish molecular clouds in crowded regions, such as the first Galactic quadrant, and velocity degenerated directions, such as the Galactic anticenter. In addition to this dimensional incompleteness, PPV observations are also subject to angular/velocity resolution and sensitivity issues, and observational effects on molecular cloud studies have been brought into focus recently (Yan et al 2021b;Louvet et al 2021;Panopoulou et al 2022).…”