2012ApJ...756...12L

We have obtained spectra of the J = 2-1 and 10-9 transitions of cyanoacetylene (HC₃N) toward a collection of positions in the most prominent filament, B213, in the Taurus molecular cloud. The analysis of the excitation conditions of these transitions reveals an average gas H₂ volume density of (1.8 ± 0.7)x10⁴/cm3. Based on column density derived from the Two Micron All Sky Survey and this volume density, the line-of-sight dimension of the high-density portion of B213 is found to be ≃0.12 pc, which is comparable to the smaller projected dimension and much smaller than the elongated dimension of B213 (∼2.4 pc). B213 is thus likely a true cylinder-like filament rather than a sheet seen edge-on. The line width and velocity gradient seen in HC₃N are also consistent with Taurus B213 being a self-gravitating filament in the early stage of either fragmentation and/or collapse.