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

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Authors : Y. Shimajiri, Ph. André, P. Palmeirim, D. Arzoumanian, A. Bracco, V. Könyves, E. Ntormousi, B. Ladjelate
Abstract : Context. Herschel observations have emphasized the role of molecular filaments in star formation. However, the origin and evolution of these filaments are not yet well understood, partly because of the lack of kinematic information.
Aims. We aim to confirm that Taurus B211/B213 filament is accreting
background cloud material from a kinematic viewpoint and to investigate the potential influence of large-scale external effects on the formation of the filament.
Methods. To examine whether the B211/B213 filament is accreting background gas due to its gravitational potential, we produced a toy accretion model and compared its predictions to the velocity patterns
observed in 12CO (1–0) and 13CO (1–0). We also examined the spatial distributions of Ha, Planck 857 GHz dust continuum, and HI emission to search for evidence of large-scale external effects.
Results. We estimated the depth of the Taurus cloud around the B211/B213 filament to be ∼0.3–0.7 pc under the assumption that the density of the gas is the same as the critical density of 13CO (1–0). Compared to a linear extent of > 10 pc in the plane of the sky, this suggests that the 3D morphology of the cloud surrounding the B211/B213 filament is sheet-like. Position-velocity (PV) diagrams observed in 12 CO (1–0) and 13 CO (1–0) perpendicular to the filament axis show that the emission from the gas surrounding B211/B213 is redshifted to the northeast of the filament and blueshifted to the southwest, respectively, and that the velocities of both components approach the velocity of the B211/B213 filament as the line of sight approaches the crest of the filament. The PV diagrams predicted by our
accretion model are in good agreement with the observed 12CO (1–0) and 13CO (1–0) PV diagrams, supporting the scenario of mass accretion into the filament proposed by Palmeirim et al. Moreover, inspection of the spatial distribution of the Hα and Planck 857 GHz emission in the Taurus-California-Perseus region on scales up to >200 pc suggests that the B211/B213 filament may have formed as a result of an expanding supershell generated by the Per OB2 association.
Conclusions. Based on these results, we propose a scenario in which the B211/B213 filament was 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.
Journal : Astronomy and Astrophysics ArXiv