The Two States of Star-Forming Clouds

Collins, David C.; Kritsuk, Alexei G.; Padoan, Paolo; Li, Hui; Xu, Hao; Ustyugov, S. D.; Norman, Michael L.

doi:10.1088/0004-637x/750/1/13

Cited by 153 publications

(285 citation statements)

References 92 publications

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“…This interpretation is confirmed by restricting the plot to prestellar cores only, as indicated by the dotted line in the figure. Such behaviour is predicted by simulations (Kritsuk et al 2011;Collins et al 2012;Federrath & Klessen 2013) which yield model PDFs similar in appearance to Fig. 8.…”

Section: Relationship To Unbound Starless Coressupporting

confidence: 74%

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

Marsh

Kirk

André

et al. 2016

Mon. Not. R. Astron. Soc.

123

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We present a catalogue of dense cores in a ∼ 4 • × 2 • field of the Taurus star-forming region, inclusive of the L1495 cloud, derived from Herschel SPIRE and PACS observations in the 70 µm, 160 µm, 250 µm, 350 µm, and 500 µm continuum bands. Estimates of mean dust temperature and total mass are derived using modified blackbody fits to the spectral energy distributions. We detect 525 starless cores of which ∼ 10-20% are gravitationally bound and therefore presumably prestellar. Our census of unbound objects is ∼ 85% complete for M > 0.015 M ⊙ in low density regions (A V < ∼ 5 mag), while the bound (prestellar) subset is ∼ 85% complete for M > 0.1 M ⊙ overall. The prestellar core mass function (CMF) is consistent with lognormal form, resembling the stellar system initial mass function, as has been reported previously. All of the inferred prestellar cores lie on filamentary structures whose column densities exceed the expected threshold for filamentary collapse, in agreement with previous reports. Unlike the prestellar CMF, the unbound starless CMF is not lognormal, but instead is consistent with a power-law form below 0.3 M ⊙ and shows no evidence for a lowmass turnover. It resembles previously reported mass distributions for CO clumps at low masses (M < ∼ 0.3 M ⊙ ). The volume density PDF, however, is accurately lognormal except at high densities. It is consistent with the effects of self-gravity on magnetized supersonic turbulence. The only significant deviation from lognormality is a high-density tail which can be attributed unambiguously to prestellar cores.

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Section: Relationship To Unbound Starless Coressupporting

confidence: 74%

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

Marsh

Kirk

André

et al. 2016

Mon. Not. R. Astron. Soc.

123

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“…number of dense regions increases and this introduces a powerlaw tail on the high-density side of the PDF (e.g., Klessen 2000;Vázquez-Semadeni et al 2008;Collins et al 2012;Girichidis et al 2014). These predictions are observationally verified for giant molecular clouds (GMCs) in the Milky Way (e.g., Lombardi et al 2010;Schneider et al 2012).…”

Section: Surface Stellar Mass Density Distributionmentioning

confidence: 85%

Hierarchical star formation across the grand-design spiral NGC 1566

Gouliermis

Elmegreen²,

Elmegreen

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate how star formation is spatially organized in the grand-design spiral NGC 1566 from deep HST photometry with the Legacy ExtraGalactic UV Survey (LEGUS). Our contour-based clustering analysis reveals 890 distinct stellar conglomerations at various levels of significance. These star-forming complexes are organized in a hierarchical fashion with the larger congregations consisting of smaller structures, which themselves fragment into even smaller and more compact stellar groupings. Their size distribution, covering a wide range in length-scales, shows a power-law as expected from scale-free processes. We explain this shape with a simple "fragmentation and enrichment" model. The hierarchical morphology of the complexes is confirmed by their mass-size relation which can be represented by a powerlaw with a fractional exponent, analogous to that determined for fractal molecular clouds. The surface stellar density distribution of the complexes shows a log-normal shape similar to that for supersonic non-gravitating turbulent gas. Between 50 and 65 per cent of the recentlyformed stars, as well as about 90 per cent of the young star clusters, are found inside the stellar complexes, located along the spiral arms. We find an age-difference between young stars inside the complexes and those in their direct vicinity in the arms of at least 10 Myr. This timescale may relate to the minimum time for stellar evaporation, although we cannot exclude the in situ formation of stars. As expected, star formation preferentially occurs in spiral arms. Our findings reveal turbulent-driven hierarchical star formation along the arms of a grand-design galaxy.

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“…Our simulations do not show the emergence of a clear power-law tail in the PDF as star formation progresses (cf. Klessen et al 2000;Vázquez-Semadeni et al 2008;Federrath et al 2008;Kritsuk et al 2011;Collins et al 2012;Federrath & Klessen 2013;Lee et al 2015), likely because our global cloud models lack resolution at the highest densities. The measured values of σ lnΣ are somewhat larger in our simulations than in nearby well-studied clouds (Schneider et al 2015), although more massive, more turbulent GMCs are likely to have broader PDFs.…”

Section: Surface Density Distributionmentioning

confidence: 99%

Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces. I. Star Formation Rate and Efficiency

Raskutti

Ostriker

Skinner

2016

ApJ

111

131

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Radiation feedback from stellar clusters is expected to play a key role in setting the rate and efficiency of star formation in giant molecular clouds (GMCs). To investigate how radiation forces influence realistic turbulent systems, we have conducted a series of numerical simulations employing the Hyperion radiation hydrodynamics solver, considering the regime that is optically thick to ultraviolet (UV) and optically thin to infrared (IR) radiation. Our model clouds cover initial surface densities between Σ cl,0 ∼ 10 − 300 M pc −2 , with varying initial turbulence. We follow them through turbulent, self-gravitating collapse, formation of star clusters, and cloud dispersal by stellar radiation. All our models display a lognormal distribution of gas surface density Σ; for an initial virial parameter α vir,0 = 2, the lognormal standard deviation is σ lnΣ = 1 − 1.5 and the star formation rate coefficient ε ff,ρ = 0.3 − 0.5, both of which are sensitive to turbulence but not radiation feedback. The net star formation efficiency ε final increases with Σ cl,0 and decreases with α vir,0 . We interpret these results via a simple conceptual framework, whereby steady star formation increases the radiation force, such that local gas patches at successively higher Σ become unbound. Based on this formalism (with fixed σ lnΣ ), we provide an analytic upper bound on ε final , which is in good agreement with our numerical results. The final star formation efficiency depends on the distribution of Eddington ratios in the cloud and is strongly increased by turbulent compression of gas.

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The Two States of Star-Forming Clouds

Cited by 153 publications

References 92 publications

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

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

Hierarchical star formation across the grand-design spiral NGC 1566

Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces. I. Star Formation Rate and Efficiency

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