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Center for AstronomyOn the nature of star-forming filaments: I Filament morphologies
Abstract
We use a suite of high resolution molecular cloud simulations carried out with the moving mesh code Arepo to explore the nature of star-forming filaments. The simulated filaments are identified and categorised from column density maps in the same manner as for recent Herschel observations. When fit with a Plummer-like profile the filaments are in excellent agreement with observations, and have shallow power-law profiles of p~2.2 without the need for magnetic support. The derived filament widths depend on the data range that is fitted. When data within 1 pc of the filament centre is fitted with a Gaussian function, the average FWHM is ~0.3 pc, in agreement with predictions for accreting filaments. However, if the fit is constructed using only data within 0.35 pc of the centre, in order to better match the procedure used to derive filament widths from Herschel observations, the resulting FWHM is only ~ 0.2 pc. This value is larger than that measured in IC 5146 and Taurus, but is similar to that found in the Planck Galactic Cold Cores and in Cygnus X. The simulated filaments have a range of widths rather than a constant value. When the column density maps are compared to the 3D gas densities, the filaments seen in column density do not belong to a single structure. Instead, they are made up of a network of short ribbon-like sub-filaments reminiscent of those seen in Taurus. The sub-filaments seen in 3D have flattening radii of the order of the Jeans radius, consistent with them being thermally supported. The sub-filaments are pre-existing within the simulated clouds, and are not primarily formed through fragmentation of the larger filament seen in column density. Instead, small filamentary clumps are swept together into a single column density structure by the large-scale collapse of the cloud. This increases the density of the sub-filaments and may induce future star formation within them.
Pre-print
A pre-print of this paper is available at arXiv1407.6716
Supplemental Data
- A movie showing slices of 0.05 pc thickness along the simulation y-axis centred on the spine of filament S1-F1-T130.The filament sections are not smooth but have considerable substructure and the peak column density does not necessarily correspond to the filament centre. This movie should be viewed in conjunction with Section 4.1 and Figure 10 of the paper.
- A movie showing a zoom around the 3D spine points for the 3D filaments found in the vicinity of S1-F1-T130. As in the previous case, we find that what appears to be a single filament when observed in projection is actually made up of a number of smaller sub-filaments. These sub-filaments are not parallel to each other but branch out at a variety of angles from one another. They also frequently cross and intersect each other. However, at the same time, the 3D spine points have a global distribution which is elongated along the $y$-axis. This movie should be viewed in conjunction with Section 4.2 and Figure 11 of the paper.
- Movies showing the formation of the filaments in the four simulations with our fiducial resolution. The filaments form from the large scale collapse within the cloud sweeping up small filaments and clumps of gas into one large column density structure.As the clouds have an irregular geometry and initial velocities, the collapse is not purely radial and there are also shearing velocities. This movie should be viewed in conjunction with Section 5.2 and Figure 14 of the paper.
- If you would like to compare your results to any of the data used in this paper please e-mail me.
