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|Title:||How the power spectrum of dust continuum images may hide the presence of a characteristic filament width||Authors:||Roy, A.
Miville-Deschênes, M. -A.
Kirk, J. M.
|Issue Date:||2019||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||626||First Page:||A76||Abstract:||Context. Herschel observations of interstellar clouds support a paradigm for star formation in which molecular filaments play a central role. One of the foundations of this paradigm is the finding, based on detailed studies of the transverse column density profiles observed with Herschel, that nearby molecular filaments share a common inner width of ∼0.1 pc. The existence of a characteristic filament width has been recently questioned, however, on the grounds that it seems inconsistent with the scale-free nature of the power spectrum of interstellar cloud images. <BR /> Aims: In an effort to clarify the origin of this apparent discrepancy, we examined the power spectra of the Herschel/SPIRE 250 μm images of the Polaris, Aquila, and Taurus-L1495 clouds in detail and performed a number of simple numerical experiments by injecting synthetic filaments in both the Herschel images and synthetic background images. <BR /> Methods: We constructed several populations of synthetic filaments of 0.1 pc width with realistic area filling factors (A<SUB>fil</SUB>) and distributions of column density contrasts (δ<SUB>c</SUB>). After adding synthetic filaments to the original Herschel images, we recomputed the image power spectra and compared the results with the original, essentially scale-free power spectra. We used the χ<SUP>2</SUP><SUB>variance</SUB> of the residuals between the best power-law fit and the output power spectrum in each simulation as a diagnostic of the presence (or absence) of a significant departure from a scale-free power spectrum. <BR /> Results: We find that χ<SUP>2</SUP><SUB>variance</SUB> depends primarily on the combined parameter δ<SUP>2</SUP><SUB>2</SUB> A<SUB>fil</SUB>. According to our numerical experiments, a significant departure from a scale-free behavior and thus the presence of a characteristic filament width become detectable in the power spectrum when δ<SUP>2</SUP><SUB>2</SUB> A<SUB>fil</SUB> ⪆ 0.1 for synthetic filaments with Gaussian profiles and δ<SUP>2</SUP><SUB>2</SUB> A<SUB>fil</SUB> ⪆ 0.4 for synthetic filaments with Plummer-like density profiles. Analysis of the real Herschel 250 μm data suggests that δ<SUP>2</SUP><SUB>2</SUB> A<SUB>fil</SUB> is ∼0.01 in the case of the Polaris cloud and ∼0.016 in the Aquila cloud, significantly below the fiducial detection limit of δ<SUP>2</SUP><SUB>2</SUB> A<SUB>fil</SUB> ∼ 0.1 in both cases. In both clouds, the observed filament contrasts and area filling factors are such that the filamentary structure contributes only ∼1/5 of the power in the image power spectrum at angular frequencies where an effect of the characteristic filament width is expected. <BR /> Conclusions: We conclude that the essentially scale-free power spectra of Herschel images remain consistent with the existence of a characteristic filament width ∼0.1 pc and do not invalidate the conclusions drawn from studies of the filament profiles.||URI:||http://hdl.handle.net/20.500.12386/28824||URL:||https://www.aanda.org/articles/aa/full_html/2019/06/aa32869-18/aa32869-18.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201832869||Bibcode ADS:||2019A&A...626A..76R||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jun 19, 2021
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