Unveiling Fiber Networks and Core Formation in the DR21 South Filament

Abstract

We present high-resolution ($\sim$1000 AU) 3 mm observations with the NOrthern Extended Millimeter Array toward the DR21 South Filament, aiming to reveal its internal fragmentation and search for deeply embedded star-forming activities. Both the continuum and molecular line emissions align well with the filament axis traced by the low-resolution ($\sim$18${}^{\prime \prime }$) column density map. The 3 mm continuum, CS (2$-$1), and HCO${}^{+}$ (1$-$0) emissions reveal continuous and diffuse structures with measured FWHM widths of 0.054, 0.029, and 0.030 pc, respectively. In contrast, the H${}^{13}$CO${}^{+}$ (1$-$0) emission appears more clumpy and localized. The non-thermal motion in the filament is predominantly subsonic to transonic. We detect 13 dense cores in NH${}_2$D (1${}_{11}-1_{01}$), three of which coincide with continuum peaks; virial analysis suggests most are gravitationally bound. Using a friend-of-friend algorithm, we identify 32, 34, and 22 velocity-coherent fibers from the CS, HCO${}^{+}$, and H${}^{13}$CO${}^{+}$ data, respectively. Compared to fibers traced by CS and HCO${}^{+}$, H${}^{13}$CO${}^{+}$ fibers are more frequently associated with NH${}_2$D cold cores and exhibit higher average mass-per-unit-length values. Differences among CS, HCO${}^{+}$, and H${}^{13}$CO${}^{+}$ emissions likely arise from variations in effective critical densities. These results are consistent with a hierarchical structure, in which the 3.6-pc DR21SF contains velocity-coherent fibers and gravitationally bound dense cores.

21 pages, 8 figures, 6 tables. Accepted for publication in The Astronomical Journal

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