1 Observatorio Astronómico Nacional (IGN), Alfonso XII 3, 28014 Madrid, Spain
2 Institute for Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
3 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
4 University of Minnesota, 116 Church St SE, Minneapolis, MN 55414, USA
Received: 24 July 2012
Accepted: 8 March 2013
Context. Core condensation is a critical step in the star-formation process, but it 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 observed L1495/B213 in C18O(1−0), N2H+(1−0), and SO(JN = 32–21) with the 14 m FCRAO telescope, and complemented the data with dust continuum observations using APEX (870 μm) and IRAM 30 m (1200 μm).
Results. From the N2H+ emission, we identify 19 dense cores, some starless and some protostellar. They are not distributed uniformly, 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 identify them automatically using a dedicated algorithm (FIVE: Friends In VElocity). Using this algorithm, we identify 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 few fertile components with higher mass-per-unit length being responsible for most cores in the cloud. On large scales, the filamentary components appear grouped into families, which we refer to as bundles.
Conclusions. Core formation in L1495/B213 has proceeded by hierarchical fragmentation. The cloud fragmented first into several pc-scale regions. Each of these regions later fragmented into velocity-coherent filaments of about 0.5 pc in length. Finally, a small number of these filaments fragmented quasi-statically and produced the individual dense cores we see today.
Key words: ISM: clouds / ISM: kinematics and dynamics / ISM: molecules / ISM: structure / stars: formation / radio lines: ISM
Based on observations carried out with the FCRAO 14 m and IRAM 30 m telescopes. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). Also based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory (ESO projects 080.C-3054 and 083.C-0453).
The Gaussian fits results presented in Sect. 5 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/554/A55
© ESO, 2013