Letter to the Editor

The width of Herschel filaments varies with distance

¹ California Institute of Technology, Mail Code 350-17, 1200 E. California Blvd, Pasadena, CA 91125, USA
e-mail: panopg@caltech.edu
² Department of Physics, Stanford University, Stanford, California 94305, USA
³ Kavli Institute for Particle Astrophysics & Cosmology, Stanford University, PO Box 2450 Stanford, CA 94305, USA
⁴ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁵ Department of Physics & Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
⁶ Chalmers University of Technology, Department of Space, Earth and Environment, 412 93 Gothenburg, Sweden
⁷ Scuola Normale Superiore di Pisa, Piazza dei Cavalieri, 7, 56126 Pisa, Italy
⁸ University of Cologne, I. Physical Institute, Zülpicher Str. 77, 50937 Cologne, Germany
⁹ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK

Received: 22 September 2021
Accepted: 15 November 2021

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.