2015A&A...574A.104T

Cloud fragmentation into dense cores is a critical step in the process of star formation. A number of recent observations show that it is connected to the filamentary structure of the gas, but the processes responsible for core formation remain mysterious. We studied the kinematics and spatial distribution of the dense gas in the L1495/B213 filamentary region of the Taurus molecular cloud with the goal of understanding the mechanism of core formation. We mapped the densest regions of L1495/B213 in N₂H⁺(1-0) and C¹⁸O(2-1) with the IRAM 30 m telescope, and complemented these data with archival dust-continuum observations from the Herschel Space Observatory. The dense cores in L1495/B213 are significantly clustered in linear chain-like groups about 0.5pc long. The internal motions in these chains are mostly subsonic and the velocity is continuous, indicating that turbulence dissipation in the cloud has occurred at the scale of the chains and not at the smaller scale of the individual cores. The chains also present an approximately constant abundance of N₂H⁺ and radial intensity profiles that can be modeled with a density law that follows a softened power law. A simple analysis of the spacing between the cores using an isothermal cylinder model indicates that the cores have likely formed by gravitational fragmentation of velocity-coherent filaments. Combining our analysis of the cores with our previous study of the large-scale C¹⁸O emission from the cloud, we propose a two-step scenario of core formation in L1495/B213. In this scenario, named ``fray and fragment'', L1495/B213 originated from the supersonic collision of two flows. The collision produced a network of intertwined subsonic filaments or fibers (fray step). Some of these fibers accumulated enough mass to become gravitationally unstable and fragment into chains of closely-spaced cores.