A complete survey of filaments in Cygnus X

TL;DR

This work presents a complete census of filaments in Cygnus X using the getsf algorithm on a Herschel-derived column-density map, yielding 2633 filaments and 6551 cores and enabling a multifaceted analysis of their properties and connections to dense cores, the Planck magnetic field, HII regions, and YSOs. The results show a typical filament width of ~0.5 pc, with over 93% of high-mass cores (>20 M_sun) on filaments, and high-mass CMF slopes of ~-2.30 for on-filament and all cores, versus ~-2.83 off-filament, indicating filaments are key sites for massive-core formation and growth via accretion. Filaments are generally perpendicular to the Planck B-field at ~2 pc scales, with a parallel alignment at low densities and a transition near A_V ≈ 10 mag, supporting a magnetically regulated formation process and a type-O converging-flow MHD-shock scenario in Cygnus X. The expansion of HII regions appears to compress gas into pc-scale filaments along bubble boundaries and intersections, aligning with a bubble–filament paradigm and the idea that HII-driven feedback shapes the filamentary network and subsequent star formation by feeding high-mass cores through filamentary reservoirs.

Abstract

Filamentary structures are widely observed in molecular clouds, yet most filament observations are biased toward case studies and small samples; a uniform census within a single giant molecular cloud is still missing. We do a complete census of filaments in Cygnus X and quantify their links to dense cores, the magnetic field (B field), and HII regions. Using the updated getsf algorithm on the Cygnus X column-density map, we extracted 2633 filaments and 6551 cores. We built CMFs for cores on and off filaments, compared filament orientations with the Planck B field, measured radial column-density profiles near HII-region boundaries, and computed distances between young stellar objects and filament spines. Filaments have a typical width of 0.5 pc in Cygnus X at a resolution of 0.12 pc and host > 93% of high-mass cores (>= 20 Msun). The on-filament CMF shows a high-mass (> 10 Msun) slope of -2.30, while the off-filament CMF is steeper (-2.83). The onCMF peak mass is well below the Bonnor-Ebert mass, whereas the outCMF peak is comparable to it. At 5' resolution, filaments are mostly perpendicular to the B field except at the lowest column densities; the transition occurs near Av = 10 mag. Prominent filaments and high-mass cores preferred to be located around HII-region boundaries or at intersections of multiple HII regions; filament profiles are steeper on the side facing the HII region. Massive-core formation depends strongly on filaments, which may provide reservoirs that feed cores via accretion. The B field likely regulates filament formation, consistent with the type-O mode (converging flows along an oblique MHD shock) and an HII-driven bubble-filament paradigm for Cygnus X.

Figures (17)

• Figure 1: Skeletons of all filaments extracted with getsf are shown by black lines. The background is the column-density map of Cygnus X, which was derived by Cao2019 with the Herschel multi-band dust-continuum-emission maps.
• Figure 2: Normalized width distribution of extracted filament skeletons (Fig. \ref{['fig:filament']}). This distribution has a peak at 0.5 pc, which indicates a typical width of the filaments in Cygnus X. The resolution 0.12 pc is also labeled as an arrow.
• Figure 3: onCMF (blue dots) and outCMF (red dots) derived from the cores on and outside of filaments, respectively (Sect. \ref{['subsec:filamentary structures and cores and CMF']}). The two different power-law slopes for the two CMFs at the high-mass end (over 10 M$_{\odot}$) are -2.30 and -2.83 for onCMF (black solid line) and outCMF (green solid line), respectively. This analysis highlights a tendency of high-mass cores to be preferentially located on filaments. The allCMF (gray dots) also has the similar power-law slope -2.30 at the high-mass end (over 10 M$_{\sun}$). The initial mass function from Kroupa2003 is shown by a dashed line.
• Figure 4: Planck B field (black segments), smoothed column-density map (5’,background), and re-extracted filaments (red solid lines) on this smoothed map.
• Figure 5: Distribution of orientation differences between filaments and B field at a resolution of 5' (2 pc). This bimodal distribution peaking at $0^{\circ}$ and $90^{\circ}$ suggests filaments tend to be perpendicular or parallel to the B field on a several-pc scale.