An ammonia spectral map of the L1495-B218 filaments in the taurus molecular cloud. II. CCS and HC ₇ N chemistry and three modes of star formation in the filaments

We present deep CCS and HC ₇ N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100 m Green Bank Telescope. We observed the L1495-B218 filaments in CCS J _N = 2 ₁ -1 ₀ and HC ₇ N J = 21-20 with a spectral resolution of 0.038 km s ^-1 and an angular resolution of 31″. We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC ₇ N emission is observed only in L1495A-N and L1521D. We find that CCS and HC ₇ N intensity peaks do not coincide with NH ₃ or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC ₇ N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines, including NH ₃ , HC ₇ N, CCS, CO, HCN, and HCO ⁺ , suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), whereas L1521D, a core embedded in a filament, is slowly contracting because of its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode).