Star and Cluster Formation in the Sh2-112 Filamentary Cloud Complex

We present the star formation activity around the emission nebula Sh2-112. At a distance of $\sim2.1$~kpc, this \ion{H}{2} complex, itself 3~pc in radius, is illuminated by the massive star (O8\,V) BD$+$45\,3216. The associated molecular cloud extends in angular scales of 2\fdg0\times0\fdg83, corresponding to linear sizes of 73~pc by 30~pc, along the Galactic longitude. The high-resolution (30\arcsec) extinction map reveals a chain of dust clumps aligned with the filament-like structure with an average extinction of $A_{V} \sim 2.78$~mag, varying up to a maximum of $\sim17$~mag. Our analysis led to identification of a rich population ($\sim 500$) of young (average age of $\sim 1$~Myr) stars, plus a numerous number ($\sim 350$) of H$\alpha$ emitters, spatially correlated with the filamentary clouds. Located near the edge of the cloud, the luminous star BD$+$45\,3216 has created an arc-like pattern as the ionizing radiation encounters the dense gas, forming a blister-shaped morphology. We found three distinct young stellar groups, all coincident with relatively dense parts of the cloud complex, signifying ongoing star formation. Moreover, the cloud filament (excitation temperature $\sim 10$~K) traced by the CO isotopologues and extending nearly $\sim 80$~pc is devoid of ionized gas except at the dense cores (excitation temperature $\sim$ 28--32~K) wherein significant ionized emission excited by OB stars (dynamical age $\sim$ 0.18--1.0~Myr) pertains. The radial velocity is dynamic (median $\sim -3.65$~km~s$^{-1}$) along the main filament, increasing from Galactic east to west, features mass flow to form the massive stars/clusters at the central hubs.Comment: 29 pages, 16 figures, 5 tables, accepted for publication in Ap

Merging Filaments and Hub Formation in the G083.097++03.270 Molecular Complex

We uncover a hub-filament system associated with massive star formation in the G083.097$+$03.270. Diagnosed with simultaneous $^{12}$CO, $^{13}$CO, and C$^{18}$O line observations, the region is found to host two distinct and elongated filaments having separate velocity components, interacting spatially and kinematically, that appear to have seeded the formation of a dense hub at the intersection. A large velocity spread at the hub in addition to clear bridging feature connecting the filaments in velocity are indicating merging of filaments. Along the filaments axis, the velocity gradient reveals a global gas motion with an increasing velocity dispersion inward to the hub signifying turbulence. Altogether, the clustering of Class I sources, a high excitation temperature, a high column density, and presence of a massive outflow at the central hub suggest enhanced star formation. We propose that merging of large-scale filaments and velocity gradients along filaments are the driving factors in the mass accumulation process at the hub that have sequentially led to the massive star formation. With two giant filaments merging to coincide with a hub therein with ongoing star formation, this site serves as a benchmark for the `filaments to clusters' star-forming paradigm.Comment: 12 pages, 7 figures, 1 table, accepted for publication in Ap