Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region

Abstract

Context. Core condensation is a critical step in the star-formation process, but is still poorly characterized observationally. Aims. We have studied the 10 pc-long L1495/B213 complex in Taurus to investigate how dense cores have condensed out of the lower-density cloud material. Methods. We have observed L1495/B213 in C18O(1–0), N2H+(1–0), and SO(JN=32–21) with the 14-m FCRAO telescope, and com-plemented the data with dust continuum observations using APEX (870 µm) and IRAM 30m (1200 µm). Results. From the N2H+ emission, we identify 19 dense cores, some starless and some protostellar. They are not distributed uni-formly, but tend to cluster with relative separations on the order of 0.25 pc. From the C18O emission, we identify multiple velocity components in the gas. We have characterized them by fitting gaussians to the spectra, and by studying the distribution of the fits in position-position-velocity space. In this space, the C18O components appear as velocity-coherent structures, and we have identified them automatically using a dedicated algorithm (FIVe: Friends In Velocity). Using this algorithm, we have identified 35 filamentary components with typical lengths of 0.5 pc, sonic internal velocity dispersions, and mass-per-unit-length close to the stability threshold of isothermal cylinders at 10 K. Core formation seems to have occurred inside the filamentary components via fragmentation, with a small number of fertile components with larger mass-per-unit-length being responsible for most cores in the cloud. At large scales, the filamentary components appear grouped into families, which we refer to as bundles.