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 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 C 18 O(1−0), N 2 H + (1−0), and SO(J N = 3 2 -2 1 ) 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 N 2 H + 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 C 18 O 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 C 18 O 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.

A census of dense cores in the Taurus L1495 cloud from theHerschelGould Belt Survey

“…If we take 0.1 pc as the mean filamentary width, then the estimated line masses of filamentary structure in the immediate vicinities of prestellar cores throughout L1495 are in the range 32 ± 15 M⊙ pc −1 . Our mean value is about a factor of two larger than the value 15 M⊙ pc −1 found by Hacar et al (2013) using N2H + observations, and the value 17 M⊙ pc −1 found by Schmalzl et al (2010) based on near-infrared extinction measurements. The reason for the discrepancy is not clear, but it is significant that all three estimates are greater than or equal to the theoretical value of 16 M⊙ pc −1 for an isothermal cylinder in pressure equilibrium at 10 K (Inutsuka & Miyama 1997).…”

“…The spatial filtering does, however, serve to show the smaller scale features superposed on the overall filament structure. Some of these features are in the form of threadlike structures which correspond very well to the velocity coherent "fibres" identified by Hacar et al (2013) in C 18 O (see Fig. 2 of André et al 2014).…”

The Link Between Turbulence, Magnetic Fields, Filaments, and Star Formation in the Central Molecular Zone Cloud G0.253+0.016

“…Indeed, star-forming cores in nearby spiral-arm clouds are often located along dense filaments (Polychroni et al 2013;Könyves et al 2015) and young star clusters tend to form at their intersections (Myers 2011;Schneider et al 2012). Recent observations and simulations of spiral-arm clouds show that filaments have coherent velocities (Hacar et al 2013Moeckel & Burkert 2015;Smith et al 2016) and orientations preferentially (but not always) perpendicular to the magnetic field (Gaensler et al 2011;Sugitani et al 2011;Hennebelle 2013;Palmeirim et al 2013;Planck Collaboration et al 2016a, 2016b, 2016cTomisaka 2014;Zhang et al 2014;Pillai et al 2015;Seifried & Walch 2015). Most importantly, filaments seem to have a nearly universal widthW 0.1 pc fil (Arzoumanian et al 2011;Juvela et al 2012;Malinen et al 2012;Palmeirim et al 2013;Benedettini et al 2015;Kirk et al 2015;Roy et al 2015;Salji et al 2015;Wang et al 2015;Kainulainen et al 2016).…”

Theoretical Models of Protostellar Binary and Multiple Systems with AMR Simulations

“…Models and methods As the initial condition, a filamentary molecular cloud is considered because recent observations have shown that molecular clouds often exhibit filamentary structures [10,11,12]. The filament is assumed to be infinitely long and in an equilibrium state where thermal pressure supports an isothermal cloud against its self-gravity.…”