An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud: II CCS & HC 7 N Chemistry and Three Modes of Star Formation in the Filaments

Abstract

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 100m 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, \& 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), while L1521D, a core embedded in a filament, is slowly contracting due to 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).