Observational signatures of end-dominated collapse in the S242 filamentary structure

Abstract

We present new CO (13CO(1-0) and C18O(1-0)) and CS(2-1) line observations of an elongated filamentary structure (length ~30 pc) in the star-forming site S242, which were taken with the OSO-20m telescope. One filament's end hosts the S242 HII region, while the other end contains Planck cold clumps. Several sub-regions are identified in the filament, and are supersonic with Mach number of 2.7-4.0. The study of the dynamical states shows supercritical nature of the sub-regions (except central part), which could not be supported by a combination of thermal and turbulent motions. Young stellar objects are seen toward the entire filament, but more concentrated toward its ends. Dense molecular cores are observed mainly toward the filament ends, and are close to virial equilibrium. Position-velocity plots trace velocity gradients (~1 km/s/pc) toward both the ends. An oscillatory pattern in velocity is also observed toward the filament, indicating its fragmentation. The collapse timescale of the filament is computed to be ~3.5 Myr. Using the 13CO data, the structure function in velocity of the filament is found to be very similar as seen in the Musca cloud for lags ~1-3 pc, and deviates from the Larson's velocity-size relationship. The observed oscillatory pattern in the structure function at higher lags suggests the existence of large-scale and ordered velocity gradients as well as the fragmentation process through accretion along the filament. Considering all the observed results along with their uncertainties, the S242 filament is a very good example of the end-dominated collapse.