Dense core formation by fragmentation of velocity-coherent filaments in L1517

By Á. Hacar, M. Tafalla, Alfonso Xii. 2011

150 citations recorded by the source corpus.

Context. Low-mass star-forming cores differ from their surrounding molecular cloud in turbulence, shape, and density structure. Aims. We aim to understand how dense cores form out of the less dense cloud material by studying the connection between these two regimes. Methods. We observed the L1517 dark cloud in C 18 O(1–0), N2H + (J = 1−0), and SO(JN = 32−21) with the FCRAO 14 m telescope, and in the 1.2 mm dust continuum with the IRAM 30 m telescope. Results. Most of the gas in the cloud lies in four filaments that have typical lengths of 0.5 pc. Five starless cores are embedded in these filaments and have chemical compositions indicative of different evolutionary stages. The filaments have radial profiles of C 18 O(1−0) emission with a central flattened region and a power-law tail, and can be fitted approximately as isothermal, pressure-supported cylinders. The filaments, in addition, are extremely quiescent. They have subsonic internal motions and are coherent in velocity over their whole length. The large-scale motions in the filaments can be used to predict the velocity inside the cores, indicating that core formation has not decoupled the dense gas kinematically from its parental material. In two filaments, these large-scale motions consist of oscillations in the velocity centroid, and a simple kinematic model suggests that they may be related to core-forming flows. Conclusions. Core formation in L1517 seems to have occurred in two steps. First, the subsonic, velocity-coherent filaments have condensed out of the more turbulent ambient cloud. Then, the cores fragmented quasi-statically and inherited the kinematics of the filaments. Turbulence dissipation has therefore occurred mostly on scales on the order of 0.5 pc or larger, and seems to have played a small role in the formation of the individual cores.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/bef76a3b8c42df9c014479712a7ce18e1127ad79

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In Astronomy and Astrophysics

1. P. Myers
2. Á. Hacar
3. M. Tafalla
4. R. Gutermuth
5. N. Evans II
6. A. Kovács
7. J. Kauffmann
8. Nicolas Peretto

In Instrumentation

1. P. Myers
2. Á. Hacar
3. M. Tafalla
4. A. Kovács
5. J. Kauffmann
6. Michael McCourt
7. A. Madigan
8. Ryan M. O’Leary

Citations in the corpus

• Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region (2013, background): “Following this approach, Hacar & Tafalla (2011) found that the gas surrounding the cores of the L1517 cloud is subsonic and quiescent, like the gas inside the dense cores, in contradiction with the predictions from models of gravoturbulent fragmentation.”
• FILAMENTARY ACCRETION FLOWS IN THE EMBEDDED SERPENS SOUTH PROTOCLUSTER (2013, background): “Hacar & Tafalla (2011) observed the low-mass 1 Radio and Geoastronomy Division, Harvard Smithsonian Center for Astrophysics, MS-42, Cambridge, MA, 02138, USA 2 Currently a Banting Fellow at the Origins Institute, McMaster University; kirkh@mcmaster.ca 3 Department of Astronomy, University of…”
• A characteristic scale for cold gas (2016, result): “In similar observations, but at lower temperature, Hacar & Tafalla (2011) and Hacar et al. (2013) demonstrate in a careful analysis that molecular filaments in the interstellar medium with strongly suprathermal line widths resolve into ∼ 10s of smaller sub-filaments, each with approximately thermal…”
• SDC13 infrared dark clouds: longitudinally collapsing filaments? (2013, background): “Several high-resolution studies of filamentary cloud kinematics have been performed in the past three years towards low-mass, nearby, star-forming regions (e.g. Duarte-Cabral et al. 2010; Hacar & Tafalla 2011; Kirk et al. 2013; Arzoumanian et al. 2013).”
• An ALMA study of the Orion Integral Filament: I. Evidence for narrow fibers in a massive cloud (2018, background): “Investigating the magnitude of the line-of-sight (l.o.s.) nonthermal velocity dispersion σNT is of fundamental importance to characterize the internal dynamical state of fibers (e.g., Hacar & Tafalla 2011).”