2022ApJ...939...46P

We present the star formation activity around the emission nebula Sh2-112. At a distance of ∼2.1 kpc, this H II 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.°0 × 0.°83, corresponding to linear sizes of 73 pc by 30 pc, along the Galactic longitude. The high-resolution (30″) extinction map reveals a chain of dust clumps aligned with the filament-like structure with an average extinction of A_V ∼ 2.78 mag, varying up to a maximum of ∼17 mag. Our analysis led to identification of a rich population (∼500) of young (average age of ∼1 Myr) stars, plus a numerous number (∼350) of Hα 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 ∼10 K) traced by the CO isotopologues and extending nearly ∼80 pc is devoid of ionized gas except at the dense cores (excitation temperature ∼28-32 K) wherein significant ionized emission excited by OB stars (dynamical age ∼0.18-1.0 Myr) pertains. The radial velocity is dynamic (median ∼-3.65 km s^–1) along the main filament, increasing from Galactic east to west, indicating mass flow to form the massive stars/clusters at the central hubs.