Radiation-driven evolution and gas kinematics of the bright-rimmed cloud SFO 25

Abstract

Bright-rimmed clouds (BRCs) are valuable laboratories for investigating how ionizing radiation from massive stars reshapes molecular clouds and influences star formation. We present a kinematic and dynamical study of the BRC SFO 25 using archival James Clerk Maxwell Telescope (JCMT)-Heterodyne Array Receiver Program (HARP) observations of the 12CO, 13CO and C18O (J = 3 → 2) transitions at an angularresolution of 14 - 15 arcsec (0.051–0.054 pc).Gaia parallaxes of young stellar objects associated with the cloud yield a revised distance placing SFO 25 behind the ionizing O7V star HD 47839, implying that ultraviolet radiation can directly affect both the head and tail. The molecular gas exhibits a pronounced head–tail velocity gradient, with the tail systematically redshifted relative to the head, inconsistent with the expectations of classical radiation-driven implosion (RDI) and suggestive of an evolved phase dominated by radiative dispersal and photoevaporation. The head is moderately denser than the tail, while a compact C18O clump associated with IRAS 06382+1017 reaches densities of ∼104 cm−3. Virial and energy analyses indicate that the head, tail, and dense clump are gravitationally unbound, with kinetic energy exceeding both gravitational binding energy and external ionized gas pressure. ClassII young stellar object candidatesidentified in the tail demonstrate thatstarformation is not confined to the dense head. Although RDI may have triggered earlier star formation in the head, it cannot readily explain the activity observed in the tail, pointing to a more complex evolutionary history than predicted by the classical RDI scenario.