Probing accretion of ambient cloud material into the Taurus B211/B213 filament

Herschel observations have emphasized the role of molecular filamentsin star formation. However, the origin and evolution of these filamentsare not yet well understood, partly because of the lack of kinematic information. To examine whether the B211/B213 filamentis accreting background gas due to its gravitational potential, we produced a toy accretion model and compared its predictions to the 12CO(1--0) and 13CO(1--0) velocity patterns. We also examined the spatial distributions of Halpha, 857 GHz continuum, and HI emission to search for evidence of large-scale external effects. We estimated the depth of the cloud around the B211/B213 filamentto be 0.3--0.7 pc under the assumption that the density of the gas is the same as the 13CO critical density. Compared to a linear extent of >10 pc in the plane of the sky, this suggests that the 3D morphology of the cloud is sheet-like. 12CO and 13CO PV diagrams perpendicular to the filamentaxis show that the emission from the gas surrounding B211/B213 is redshifted to the northeast of the filamentand blueshiftedto the southwest, respectively, and that the velocities of both components approach the filamentvelocity as the line of sight approaches the filamentcrest. The PV diagrams predicted by our accretion model are in good agreement with the observed 12CO and 13CO PV diagrams, supporting the scenario of mass accretion into the filamentproposed by Palmeirim et al. Moreover, inspection of the distribution of the Halpha and 857 GHz emission in the Taurus-California-Perseus region suggests that the B211/B213 filamentmay have formed as a result of an expanding supershell generated by the Per OB2 association. Based on these results, we propose a scenario in which the B211/B213 filamentwas initially formed by large-scale compression of HI gas and then is now growing in mass due to the gravitational accretion of ambient cloud molecular gas.