The Structure of an 80 pc Long Massive Filament

TL;DR

This paper maps the ~80 pc massive filament G24 using multi-tracer molecular line data and Herschel dust continuum to characterize its three-dimensional structure and fragmentation. By deriving LTE column densities from ^13CO, C^18O, and N2H+, and constructing a high-resolution N(H_2) map from dust, the study assesses width, thickness along the line of sight, and line mass, finding a thickness of ~2.2 pc and deconvolved widths of ~0.8–2.8 pc that depend on tracer. The velocity field shows oscillatory longitudinal profiles with multiple characteristic wavelengths, suggesting velocity structure more complex than simple fragmentation-driven flows, while fragmentation analyses indicate a potential two-tier pattern with clump spacings around ~1.9–3.6 pc and groups separated by ~3.3–3.7 pc. Collectively, G24 appears near virial equilibrium with regional gravitational binding and exhibits fragmentation behavior consistent with, but not fully explained by, an infinite isothermal cylinder, pointing to additional processes such as magnetic or large-scale flows shaping its evolution.

Abstract

Using new Institut de Radioastronomie Millimétrique (IRAM) 30m telescope $\rm N_2H^+$, $\rm C^{18}O$ $J$=1-0 and Atacama Pathfinder Experiment (APEX) telescope $\rm ^{13}CO$ and $\rm C^{18}O$ $J$=2-1 maps together with archival far-infrared continuum data, and $\rm ^{12}CO$, and $\rm ^{13}CO$ $J$=1-0 data, we present a comprehensive analysis of the massive filament CFG024.00$+$0.48 (G24) across clump-to-cloud scales. Our results show that G24 is an $\sim$80 pc giant filament with a total mass of $\sim$$10^5$ M$_{\odot}$. In the different tracers the filament width is measured to be about $\sim$2 times the beam size of the observations, as expected for power-law density distributions, giving beam-deconvolved widths in the range from 0.8 to 2.8 pc. We determine a line-of-sight thickness of $\sim$2.2 pc demonstrating that G24 is not an edge-on, flatten structure. The virial parameter obtained from line mass ($α_{\rm line,vir}=M_{\rm line,vir}/M_{\rm line}$) from the $\rm C^{18}O$ (1-0) data is 0.85, and that obtained from $Herschel$-based H$_2$ column density is 0.52, suggesting G24 is globally close to virial equilibrium. The distribution of the 40 dust clumps appears to have a ''two-tier'' fragmentation pattern. For the clump groups, the separation, with a mean/median of 3.68/3.46 pc, is very close to expected length associated with the maximum fragmentation growth rate of $λ_{\rm max}=3.55 \pm0.32$ pc estimated for the dust. However, the longitudinal centroid velocity profiles of $\rm C^{18}O$ and $\rm N_2H^+$ show oscillation patterns with wavelengths of 9.8$\pm$0.1 pc and 9.9$\pm$0.1 pc, respectively. This is $\sim$2 times larger than the corresponding values of $λ_{\rm max}$ of 4.96$\pm$0.63 pc and 4.65$\pm$1.34 pc, respectively. This suggests that the velocity structure is not dominated by flows directly associated with the fragmentation seen in the dust emission.

Figures (25)

• Figure 1: Three colour-composite map of the G24 filament. Red represents 250 $\mu$m continuum emission obtained from the Herschel Hi-GAL survey, green indicates the $Spitzer$-MIPS 24 $\mu$m continuum emission, and blue is the $Spitzer$-IRAC 8 $\mu$m emission. The white contours superimposed on the map are the 21 cm radio continuum emission from VGPS, with levels of [20.5, 25, 30] K. The cyan contour is the region observed by the IRAM 30 m telescope, and the yellow dotted-dashed contour is the region observed by the APEX 12 m telescope. The region observed by the PMO 13.7 m millimetre telescope is larger than the FOV of the presented map and is not shown. The 5 pc scale indicator on the upper left corner is estimated by adopting a distance of 5.2 kpc.
• Figure 2: An overview of the integrated intensity maps of molecules in Table \ref{['tab: mol_info']}. The velocity range for integration is shown in the upper left corner of each panel, and the beam size ($\theta_{\rm HPBW}$) is shown in the lower right corner. The contours depict the intensity of 3 and 5 times the noise level.
• Figure 3: (a) H2 column density map derived from the ^13CO (1--0) data with contours of [0.8, 1.5, 2.5, 3.5, 4.5]$\rm \times 10^{22}$$\rm cm^{-2}$. (b) H2 column density map derived from the C^18O (1--0) data with the same contours as panel (a). (c) The Herschel-based H2 column density ($N$(H2)$_{Herschel}$) map at a resolution of $\sim$18.2$\rm ^{\prime\prime}$ , superimposed 40 clumps ("leaves") identified by astrodendro. The $N$(H2)$_{Herschel}$ map displayed here is the original map with background. The identified clumps are marked with orange polygons, and the black ellipses are projections. The number of the clumps is labelled in black. Four massive clumps with high surface densities (C3, C11, C32, and C34) are labelled in red. Panel (c) also displays zoomed-in views of the clumps to show their morphology.
• Figure 4: The skeleton (red curve), boundary (white contour) of G24 and paths of transverse slices, colour-coded by the FWHM of the multiple-component Gaussian model. The background is the integrated intensity map of C^18O (1--0) with the integral range of 90.5--99.0 $\rm \, km\ s^{-1}$. Clumps are superimposed on the figure and marked by black ellipses.
• Figure 5: The spatial resolution of the molecular data versus beam-deconvolved widths. The red crosses are the data from this study (G24), and blue circles indicate the data from Shimajiri_2023AnA...672A.133S (NGC 2024). The spatial resolution and filament width are in pc units by adopting the distance of 5.2 kpc for G24 and 400 pc for NGC 2024. The data from Shimajiri_2023AnA...672A.133S are shown with abbreviations for ease of presentation, where $H$ denotes $Herschel$ and A denotes ArTéMiS.