Direct Observation of a Sharp Transition to Coherence in Dense Cores

Pineda, Jaime E.; Goodman, Alyssa A.; Arce, Héctor G.; Caselli, P.; Foster, Jonathan B.; Myers, Philip C.; Rosolowsky, Erik

doi:10.1088/2041-8205/712/1/l116

Cited by 182 publications

(228 citation statements)

References 42 publications

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“…Our finding of velocity coherence on scales larger than a core would seem to contradict the recent results from Pineda et al (2010), who claim to have detected of the transition between the coherent and turbulent regimes in a core with observations of the B5 region in Perseus. We note, however, that although these authors associate the velocity coherent region with a dense core, one can see in their in B5 is elongated and has a length of about 0.5 pc, similar to our L1517 filaments.…”

Section: Velocity Coherent Filamentscontrasting

confidence: 99%

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

Hacar

Tafalla

2011

A&A

194

237

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

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Section: Velocity Coherent Filamentscontrasting

confidence: 99%

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

Hacar

Tafalla

2011

A&A

194

237

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“…Towards N, S, A2 and the diffuse intracluster emission of the main filament, the ratio is mostly in between 2 and 3, suggesting that the gas is more quiescent here but still with a dominant non-thermal contibution. In particular, we highlight the clear drop in the ratio σ nth /σ th at the edge of core S, which resambles the sharp transition in the gas turbulence observed inside and out of the low-mass dense core Barnard 5 (Pineda et al 2010). …”

Section: Non-thermal Contribution To the Velocity Dispersionmentioning

confidence: 61%

Temperature and kinematics of protoclusters with intermediate and high-mass stars: the case of IRAS 05345+3157

Fontani

Caselli

Zhang

et al. 2012

A&A

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Context. Improving our understanding of the complex star formation process in clusters requires studies of star-forming clouds to search for dependencies of the physical properties on environmental variables, such as overall density, stellar crowding and feedback from massive (proto-)stars. Aims. We aim to map at small spatial scales the temperature and the velocity field in the protocluster associated with IRAS 05345+3157, which contains both intermediate-/high-mass protostellar candidates and starless condensations, and is thus an excellent location to investigate the role of massive protostars on protocluster evolution. Methods. We observed the ammonia (1, 1) and (2, 2) inversion transitions with the VLA. Ammonia is the best thermometer for dense and cold gas, and the observed transitions have critical densities able to trace the kinematics of the intracluster gaseous medium. Results. The ammonia emission is extended and distributed in two filamentary structures. The starless condensations are colder than the star-forming cores, but the gas temperature across the whole protocluster is higher (by a factor of 1.3−1.5) than that measured typically in both infrared dark clouds and low-mass protoclusters. The non-thermal contribution to the observed line broadening is at least a factor of 2 larger than the expected thermal broadening even in starless condensations, contrary to the close-to-thermal line widths measured in low-mass quiescent dense cores. The NH 3 /N 2 H + abundance ratio is greatly enhanced (a factor of 10) in the pre-stellar core candidates, probably due to freeze-out of most molecular species heavier than He. Conclusions. The more massive and evolved objects likely play a dominant role in the physical properties and kinematics of the protocluster. The high level of turbulence and the fact that the measured core masses are larger than the expected thermal Jeans masses indicate that turbulence likely was an important factor in the initial fragmentation of the parental clump and can provide support against further fragmentation of the cores.

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“…This lower level of turbulence may account for a reduced hot gas component, if the hot gas components in the C1, F1, and F2 clumps are due to turbulent dissipation. The lower turbulent state of G2 may be related to its evolved state, given that a transition to coherence is seen in move evolved, lower mass prestellar cores (Pineda et al 2010). The G2 clump also has almost twice the D/H ratio of the other three clumps as measured from the ratio of N 2 D + and N 2 H + (Fontani et al 2011) and an order of magnitude larger D/H ratio measured from NH 3 and NH 2 D (Fontani et al 2015), thus suggesting that the G2 clump is cooler and potentially more evolved.…”

Section: Discussionmentioning

confidence: 99%

Mid-JCO shock tracing observations of infrared dark clouds. I.

Pon¹,

Caselli²,

Johnstone³

et al. 2015

A&A

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Infrared dark clouds (IRDCs) are dense, molecular structures in the interstellar medium that can harbour sites of high-mass star formation. IRDCs contain supersonic turbulence, which is expected to generate shocks that locally heat pockets of gas within the clouds. We present observations of the CO J = 8-7, 9-8, and 10-9 transitions, taken with the Herschel Space Observatory, towards four dense, starless clumps within IRDCs (C1 in G028.37+00.07, F1 and F2 in G034.43+0007, and G2 in G034.77-0.55). We detect the CO J = 8-7 and 9-8 transitions towards three of the clumps (C1, F1, and F2) at intensity levels greater than expected from photodissociation region (PDR) models. The average ratio of the 8-7 to 9-8 lines is also found to be between 1.6 and 2.6 in the three clumps with detections, significantly smaller than expected from PDR models. These low line ratios and large line intensities strongly suggest that the C1, F1, and F2 clumps contain a hot gas component not accounted for by standard PDR models. Such a hot gas component could be generated by turbulence dissipating in low velocity shocks.

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Direct Observation of a Sharp Transition to Coherence in Dense Cores

Cited by 182 publications

References 42 publications

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

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

Temperature and kinematics of protoclusters with intermediate and high-mass stars: the case of IRAS 05345+3157

Mid-JCO shock tracing observations of infrared dark clouds. I.

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