Abstract:
We present a molecular line study of the Sh2-138 (IRAS 22308+5812) hub-filament system with the aim of
investigating its structure and kinematics. Archival CO molecular line data from the Canadian Galactic Plane
Survey (CO(J = 1–0)) for the wider region (∼50′ × 50′) and the James Clerk Maxwell Telescope (CO(3–2), 13CO(3–2), and C18O(3–2)) for the central portion (∼5′ × 5′) have been utilized. Analysis of the CO(1–0) spectra
for the extended region in conjunction with the identification of the hub and filament using a column density map
and the getsf tool, respectively, reveals a complex structure with the spectral extraction for the central position
displaying multiple velocity components. Based on the Herschel 70 μm warm dust emission, one of the filaments
in the extended region was inferred to be associated with active star formation, and is host to a Bolocam 1.1 mm
clump of ∼1606 M☉. An integrated intensity map of 13CO(3–2) emission, constructed from clumps detected at
above 5σ in position–position–velocity space, reveals three filamentary structures (labeled the western filament
(W-f), southwestern filament (SW-f), and southeast filament (SE-f)) in the central portion. Velocity gradients
observed in 13CO(3–2) position–velocity slices point to longitudinal gas flow along the filaments into the central
region. Filaments W-f, SW-f, and SE-f were calculated to have observed line masses of ∼32, 33.5, and 50 M☉
pc−1
, respectively. The cloud was found to be dominated by supersonic and nonthermal motions, with high Mach
numbers (3) and a low thermal-to-nonthermal pressure ratio (∼0.01–0.1).
