A model of cloud fragmentation

Field, George B.; Blackman, Eric G.; Keto, Eric

doi:10.1111/j.1365-2966.2007.12609.x

Cited by 62 publications

(65 citation statements)

References 69 publications

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“…We propose that this process is universal and makes significant contributions to the turbulent energy on all scales (see also Field et al, 2008). When cosmic structures grow, they gain mass via accretion.…”

Section: Accretion Onto the Galaxymentioning

confidence: 94%

Physical Processes in the Interstellar Medium

Klessen

Glover

2015

Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality

160

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Interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ISM). Understanding its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. Galaxy formation and evolution, the formation of stars, cosmic nucleosynthesis, the origin of large complex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental building blocks of planets, all these processes are intimately coupled to the physics of the interstellar medium. However, despite its importance, its structure and evolution is still not fully understood. Observations reveal that the interstellar medium is highly turbulent, consists of different chemical phases, and is characterized by complex structure on all resolvable spatial and temporal scales. Our current numerical and theoretical models describe it as a strongly coupled system that is far from equilibrium and where the different components are intricately linked together by complex feedback loops. Describing the interstellar medium is truly a multi-scale and multi-physics problem. In these lecture notes we introduce the microphysics necessary to better understand the interstellar medium. We review the relations between large-scale and small-scale dynamics, we consider turbulence as one of the key drivers of galactic evolution, and we review the physical processes that lead to the formation of dense molecular clouds and that govern stellar birth in their interior.

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Section: Accretion Onto the Galaxymentioning

confidence: 94%

Physical Processes in the Interstellar Medium

Klessen

Glover

2015

Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality

160

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“…When trying to understand the initial conditions of (high-mass) star-formation, cloud fragmentation is one of the most important properties to be studied (Field et al 2008). Indeed, our interferometer observations show that each SCUBA clump fragments into several cores.…”

Section: Fragmentationmentioning

confidence: 99%

Probing the initial conditions of high-mass star formation

Pillai

Kauffmann

Wyrowski

et al. 2011

A&A

138

184

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Most work on high-mass star formation has focused on observations of young massive stars in protoclusters. Very little is known about the preceding stage. Here, we present a new high-resolution study of pre-protocluster regions in tracers exclusively probing the coldest and dense gas (NH 2 D). The two target regions G29.96−0.02 and G35.20−1.74 (W48) are drawn from the SCAMPS project, which searches for pre-protoclusters near known ultracompact Hii regions. We used our data to constrain the chemical, thermal, kinematic, and physical conditions (i.e., densities) in G29.96e and G35.20w. NH 3 , NH 2 D, HCO + , and continuum emission were mapped using the VLA, PdBI, and BIMA. In particular, NH 2 D is a unique tracer of cold, precluster gas at high densities, while NH 3 traces both the cold and warm gas of modest-to-high densities. In G29.96e, Spitzer images reveal two massive filaments, one of them in extinction (infrared dark cloud). Dust and line observations reveal fragmentation into multiple massive cores strung along filamentary structures. Most of these are cold (<20 K), dense (>10 5 cm −3 ) and highly deuterated ([NH 2 D/NH 3 ] > 6%). In particular, we observe very low line widths in NH 2 D (FWHM 1 km s −1 ). These are very narrow lines that are unexpected towards a region forming massive stars. Only one core in the center of each filament appears to be forming massive stars (identified by the presence of masers and massive outflows); however, it appears that only a few such stars are currently forming (i.e., just a single Spitzer source per region). These multi-wavelength, high-resolution observations of high-mass pre-protocluster regions show that the target regions are characterized by (i) turbulent Jeans fragmentation of massive clumps into cores (from a Jeans analysis); (ii) cores and clumps that are "over-bound/subvirial", i.e. turbulence is too weak to support them against collapse, meaning that (iii) some models of monolithic cloud collapse are quantitatively inconsistent with data; (iv) accretion from the core onto a massive star, which can (for observed core sizes and velocities) be sustained by accretion of envelope material onto the core, suggesting that (similar to competitive accretion scenarios) the mass reservoir for star formation is not necessarily limited to the natal core; (v) high deuteration ratios ([NH 2 D/NH 3 ] > 6%), which make the above discoveries possible; (vi) and the destruction of NH 2 D toward embedded stars.

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“…The first one is a turbulenceregulated scenario, where a high level of micro-turbulence acts as an effective additional thermal pressure to balance gravity (e.g., McKee & Tan 2002). In the second one, massive cores form and evolve via highly dynamical processes (e.g., Bonnell & Bate 2006;Vázquez-Semadeni et al 2007;Heitsch et al 2008;Hennebelle et al 2008;Klessen & Hennebelle 2010), where convergent flows driven by large-scale turbulence, gravity, and Galactic motions create dense structures down to small scales by shock dissipation at their stagnation points (e.g., Field et al 2008;Vázquez-Semadeni et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Convergent Flows and Low-Velocity Shocks in Dr21(oh)

Csengeri

Bontemps

Schneider

et al. 2011

ApJ

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DR21(OH) is a pc-scale massive, ∼7000 M clump hosting three massive dense cores (MDCs) at an early stage of their evolution. We present a high angular resolution mosaic, covering ∼70 × 100 , with the IRAM Plateau de Bure Interferometer at 3 mm to trace the dust continuum emission and the N 2 H + (J = 1-0) and CH 3 CN (J = 5-4) molecular emission. The cold, dense gas traced by the compact emission in N 2 H + is associated with the three MDCs and shows several velocity components toward each MDC. These velocity components reveal local shears in the velocity fields which are best interpreted as convergent flows. Moreover, we report the detection of weak extended emission from CH 3 CN at the position of the N 2 H + velocity shears. We propose that this extended CH 3 CN emission is tracing warm gas associated with the low-velocity shocks expected at the location of convergence of the flows where velocity shears are observed. This is the first detection of low-velocity shocks associated with small (subparsec) scale convergent flows which are proposed to be at the origin of the densest structures and of the formation of (high-mass) stars. In addition, we propose that MDCs may be active sites of star formation for more than a crossing time as they continuously receive material from larger scale flows as suggested by the global picture of dynamical, gravity-driven evolution of massive clumps which is favored by the present observations.

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A model of cloud fragmentation

Cited by 62 publications

References 69 publications

Physical Processes in the Interstellar Medium

Physical Processes in the Interstellar Medium

Probing the initial conditions of high-mass star formation

Convergent Flows and Low-Velocity Shocks in Dr21(oh)

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