The Cloud Factory I: Generating resolved filamentary molecular clouds from galactic-scale forces

ABSTRACT We introduce a new suite of simulations, ‘The Cloud Factory’, which self-consistently forms molecular cloud complexes at high enough resolution to resolve internal substructure (up to 0.25 M⊙ in mass) all while including galactic-scale forces. We use a version of the arepo code modified to include a detailed treatment of the physics of the cold molecular ISM, and an analytical galactic gravitational potential for computational efficiency. The simulations have nested levels of resolution, with the lowest layer tied to tracer particles injected into individual cloud complexes. These tracer refinement regions are embedded in the larger simulation so continue to experience forces from outside the cloud. This allows the simulations to act as a laboratory for testing the effect of galactic environment on star formation. Here we introduce our method and investigate the effect of galactic environment on filamentary clouds. We find that cloud complexes formed after a clustered burst of feedback have shorter lengths and are less likely to fragment compared to quiescent clouds (e.g. the Musca filament) or those dominated by the galactic potential (e.g. Nessie). Spiral arms and differential rotation preferentially align filaments, but strong feedback randomizes them. Long filaments formed within the cloud complexes are necessarily coherent with low internal velocity gradients, which has implications for the formation of filamentary star-clusters. Cloud complexes formed in regions dominated by supernova feedback have fewer star-forming cores, and these are more widely distributed. These differences show galactic-scale forces can have a significant impact on star formation within molecular clouds.

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Simulating star clusters across cosmic time – II. Escape fraction of ionizing photons from molecular clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa165 ◽

2020 ◽

Vol 492 (4) ◽

pp. 4858-4873 ◽

Cited By ~ 5

Author(s):

Chong-Chong He ◽

Massimo Ricotti ◽

Sam Geen

Keyword(s):

Star Formation ◽

Ionizing Radiation ◽

Molecular Clouds ◽

Globular Clusters ◽

Compact Star ◽

Star Clusters ◽

Cosmic Time ◽

Star Cluster ◽

Star Forming ◽

Radiation Feedback

ABSTRACT We calculate the hydrogen- and helium-ionizing radiation escaping star-forming molecular clouds, as a function of the star cluster mass and compactness, using a set of high-resolution radiation-magnetohydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds. In these simulations, presented in He et al., the formation of individual massive stars is well resolved, and their UV radiation feedback and lifetime on the main sequence are modelled self-consistently. We find that the escape fraction of ionizing radiation from molecular clouds, $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ , decreases with increasing mass of the star cluster and with decreasing compactness. Molecular clouds with densities typically found in the local Universe have negligible $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ , ranging between $0.5{{\ \rm per\ cent}}$ and $5{{\ \rm per\ cent}}$. 10 times denser molecular clouds have $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ $\approx 10{{\ \rm per\ cent}}{-}20{{\ \rm per\ cent}}$, while 100× denser clouds, which produce globular cluster progenitors, have $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ $\approx 20{{\ \rm per\ cent}}{-}60{{\ \rm per\ cent}}$. We find that $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ increases with decreasing gas metallicity, even when ignoring dust extinction, due to stronger radiation feedback. However, the total number of escaping ionizing photons decreases with decreasing metallicity because the star formation efficiency is reduced. We conclude that the sources of reionization at z > 6 must have been very compact star clusters forming in molecular clouds about 100× denser than in today’s Universe, which lead to a significant production of old globular clusters progenitors.

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The Supernova – ISM/Star-formation interplay

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313009575 ◽

2013 ◽

Vol 9 (S296) ◽

pp. 265-272

Author(s):

Gerhard Hensler

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Molecular Clouds ◽

Numerical Models ◽

Evolutionary Models ◽

Star Forming ◽

Supernova Explosions ◽

Representative Selection ◽

Supernova Feedback ◽

Selection Of

AbstractSupernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the complexity of investigations aiming at understanding the interchange between supernova explosions with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and are applying multiple recipes of these parameters, only a representative selection of studies can be discussed here.

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Properties and rotation of molecular clouds in M 33

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732405 ◽

2018 ◽

Vol 612 ◽

pp. A51 ◽

Cited By ~ 14

Author(s):

J. Braine ◽

E. Rosolowsky ◽

P. Gratier ◽

E. Corbelli ◽

K.-F. Schuster

Keyword(s):

Mass Spectrum ◽

Star Formation ◽

Molecular Clouds ◽

Mass Spectra ◽

Rotation Period ◽

Gravitational Potential Energy ◽

Galactic Rotation ◽

Galactocentric Distance ◽

Star Forming ◽

Velocity Gradients

The sample of 566 molecular clouds identified in the CO(2–1) IRAM survey covering the disk of M 33 is explored in detail. The clouds were found using CPROPS and were subsequently catalogued in terms of their star-forming properties as non-star-forming (A), with embedded star formation (B), or with exposed star formation (C, e.g., presence of Hα emission). We find that the size-linewidth relation among the M 33 clouds is quite weak but, when comparing with clouds in other nearby galaxies, the linewidth scales with average metallicity. The linewidth and particularly the line brightness decrease with galactocentric distance. The large number of clouds makes it possible to calculate well-sampled cloud mass spectra and mass spectra of subsamples. As noted earlier, but considerably better defined here, the mass spectrum steepens (i.e., higher fraction of small clouds) with galactocentric distance. A new finding is that the mass spectrum of A clouds is much steeper than that of the star-forming clouds. Further dividing the sample, this difference is strong at both large and small galactocentric distances and the A vs. C difference is a stronger effect than the inner vs. outer disk difference in mass spectra. Velocity gradients are identified in the clouds using standard techniques. The gradients are weak and are dominated by prograde rotation; the effect is stronger for the high signal-to-noise clouds. A discussion of the uncertainties is presented. The angular momenta are low but compatible with at least some simulations. Finally, the cloud velocity gradients are compared with the gradient of disk rotation. The cloud and galactic gradients are similar; the cloud rotation periods are much longer than cloud lifetimes and comparable to the galactic rotation period. The rotational kinetic energy is 1–2% of the gravitational potential energy and the cloud edge velocity is well below the escape velocity, such that cloud-scale rotation probably has little influence on the evolution of molecular clouds.

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Supernova Feedback on the Interstellar Medium and Star Formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311000561 ◽

2010 ◽

Vol 6 (S270) ◽

pp. 309-317

Author(s):

Gerhard Hensler

Keyword(s):

Star Formation ◽

Interstellar Medium ◽

Molecular Clouds ◽

Numerical Models ◽

Evolutionary Models ◽

Star Forming ◽

Hot Gas ◽

Representative Selection ◽

Supernova Feedback ◽

Selection Of

AbstractSupernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the development of the complexity of investigations aiming at understanding the interchange between supernovae and their released hot gas with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and apply multiple recipes of these parameters, only a representative selection of studies can be discussed here.

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Disruption of giant molecular clouds and formation of bound star clusters under the influence of momentum stellar feedback

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1271 ◽

2019 ◽

Vol 487 (1) ◽

pp. 364-380 ◽

Cited By ~ 17

Author(s):

Hui Li ◽

Mark Vogelsberger ◽

Federico Marinacci ◽

Oleg Y Gnedin

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Star Clusters ◽

Giant Molecular Clouds ◽

Density Profiles ◽

Stellar Feedback ◽

Wide Range ◽

Gas Removal ◽

Formation Efficiency ◽

Stellar Density

Abstract Energetic feedback from star clusters plays a pivotal role in shaping the dynamical evolution of giant molecular clouds (GMCs). To study the effects of stellar feedback on the star formation efficiency of the clouds and the dynamical response of embedded star clusters, we perform a suite of isolated GMC simulations with star formation and momentum feedback subgrid models using the moving-mesh hydrodynamics code Arepo. The properties of our simulated GMCs span a wide range of initial mass, radius, and velocity configurations. We find that the ratio of the final stellar mass to the total cloud mass, ϵint, scales strongly with the initial cloud surface density and momentum feedback strength. This correlation is explained by an analytic model that considers force balancing between gravity and momentum feedback. For all simulated GMCs, the stellar density profiles are systematically steeper than that of the gas at the epochs of the peaks of star formation, suggesting a centrally concentrated stellar distribution. We also find that star clusters are always in a sub-virial state with a virial parameter ∼0.6 prior to gas expulsion. Both the sub-virial dynamical state and steeper stellar density profiles prevent clusters from dispersal during the gas removal phase of their evolution. The final cluster bound fraction is a continuously increasing function of ϵint. GMCs with star formation efficiency smaller than 0.5 are still able to form clusters with large bound fractions.

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Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2062 ◽

2020 ◽

Vol 497 (3) ◽

pp. 3830-3845 ◽

Cited By ~ 1

Author(s):

Hajime Fukushima ◽

Hidenobu Yajima ◽

Kazuyuki Sugimura ◽

Takashi Hosokawa ◽

Kazuyuki Omukai ◽

...

Keyword(s):

Star Formation ◽

Massive Stars ◽

Cluster Formation ◽

Star Clusters ◽

Star Cluster ◽

Star Forming ◽

Dynamical Time ◽

Low Metallicity ◽

Higher Temperature ◽

Dust Attenuation

ABSTRACT We study star cluster formation in various environments with different metallicities and column densities by performing a suite of 3D radiation hydrodynamics simulations. We find that the photoionization feedback from massive stars controls the star formation efficiency (SFE) in a star-forming cloud, and its impact sensitively depends on the gas metallicity Z and initial cloud surface density Σ. At Z = 1 Z⊙, SFE increases as a power law from 0.03 at Σ = 10 M⊙ pc−2 to 0.3 at $\Sigma = 300\,\mathrm{M}_{\odot }\, {\rm pc^{-2}}$. In low-metallicity cases $10^{-2}\!-\!10^{-1}\, \mathrm{Z}_{\odot }$, star clusters form from atomic warm gases because the molecule formation time is not short enough with respect to the cooling or dynamical time. In addition, the whole cloud is disrupted more easily by expanding H ii bubbles that have higher temperature owing to less efficient cooling. With smaller dust attenuation, the ionizing radiation feedback from nearby massive stars is stronger and terminate star formation in dense clumps. These effects result in inefficient star formation in low-metallicity environments: the SFE drops by a factor of ∼3 at Z = 10−2 Z⊙ compared to the results for Z = 1 Z⊙, regardless of Σ. Newborn star clusters are also gravitationally less bound. We further develop a new semi-analytical model that can reproduce the simulation results well, particularly the observed dependencies of the SFEs on the cloud surface densities and metallicities.

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A Guide to Comparisons of Star Formation Simulations with Observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311000901 ◽

2010 ◽

Vol 6 (S270) ◽

pp. 511-519 ◽

Cited By ~ 2

Author(s):

Alyssa A. Goodman

Keyword(s):

Star Formation ◽

Spectral Line ◽

Molecular Clouds ◽

Direct Relationship ◽

Statistical Tests ◽

Random Processes ◽

Mass Function ◽

Star Forming ◽

Star Forming Regions ◽

Taste Testing

AbstractWe review an approach to observation-theory comparisons we call “Taste-Testing.” In this approach, synthetic observations are made of numerical simulations, and then both real and synthetic observations are “tasted” (compared) using a variety of statistical tests. We first lay out arguments for bringing theory to observational space rather than observations to theory space. Next, we explain that generating synthetic observations is only a step along the way to the quantitative, statistical, taste tests that offer the most insight. We offer a set of examples focused on polarimetry, scattering and emission by dust, and spectral-line mapping in star-forming regions. We conclude with a discussion of the connection between statistical tests used to date and the physics we seek to understand. In particular, we suggest that the “lognormal” nature of molecular clouds can be created by the interaction of many random processes, as can the lognormal nature of the IMF, so that the fact that both the “Clump Mass Function” (CMF) and IMF appear lognormal does not necessarily imply a direct relationship between them.

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Field spheroid-dominated galaxies in a Λ-CDM Universe

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732302 ◽

2018 ◽

Vol 614 ◽

pp. A85 ◽

Cited By ~ 4

Author(s):

M. S. Rosito ◽

S. E. Pedrosa ◽

P. B. Tissera ◽

V. Avila-Reese ◽

I. Lacerna ◽

...

Keyword(s):

Star Formation ◽

Cold Dark Matter ◽

Early Type ◽

Mass Growth ◽

Star Forming ◽

Quenching Mechanisms ◽

Formation And Evolution ◽

Dynamical Properties ◽

Open Question ◽

Supernova Feedback

Context. Understanding the formation and evolution of early-type, spheroid-dominated galaxies is an open question within the context of the hierarchical clustering scenario, particularly in low-density environments. Aims. Our goal is to study the main structural, dynamical, and stellar population properties and assembly histories of field spheroid-dominated galaxies formed in a Λ-cold dark matter (Λ-CDM) scenario to assess to what extent they are consistent with observations. Methods. We selected spheroid-dominated systems from a Λ-CDM simulation that includes star formation (SF), chemical evolution, and supernova feedback. The sample is made up of 18 field systems with MStar ≲ 6 × 1010M⊙ that are dominated by the spheroid component. For this sample we estimated the fundamental relations of ellipticals and compared them with current observations. Results. The simulated spheroid galaxies have sizes that are in good agreement with observations. The bulges follow a Sersic law with Sersic indexes that correlate with the bulge-to-total mass ratios. The structural-dynamical properties of the simulated galaxies are consistent with observed Faber–Jackson, fundamental plane, and Tully–Fisher relations. However, the simulated galaxies are bluer and with higher star formation rates (SFRs) than the observed isolated early-type galaxies. The archaeological mass growth histories show a slightly delayed formation and more prominent inside-out growth mode than observational inferences based on the fossil record method. Conclusions. The main structural and dynamical properties of the simulated spheroid-dominated galaxies are consistent with observations. This is remarkable since our simulation has not been calibrated to match them. However, the simulated galaxies are blue and star-forming, and with later stellar mass growth histories compared to observational inferences. This is mainly due to the persistence of extended discs in the simulations. The need for more efficient quenching mechanisms able to avoid further disc growth and SF is required in order to reproduce current observational trends.

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Spectral shifting strongly constrains molecular cloud disruption by radiation pressure on dust

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731698 ◽

2018 ◽

Vol 611 ◽

pp. A70 ◽

Cited By ~ 13

Author(s):

Stefan Reissl ◽

Ralf S. Klessen ◽

Mordecai-Mark Mac Low ◽

Eric W. Pellegrini

Keyword(s):

Star Formation ◽

Radiation Pressure ◽

Formation Process ◽

Molecular Clouds ◽

Far Infrared ◽

Young Star ◽

Star Forming ◽

Grain Sizes ◽

Single Temperature ◽

Spectral Shifting

Aim. We aim to test the hypothesis that radiation pressure from young star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process.Methods. We performed multi-frequency, 3D, radiative transfer calculations including both scattering and absorption and re-emission to longer wavelengths for model clouds with masses of 104–107 M⊙, containing embedded clusters with star formation efficiencies of 0.009–91%, and varying maximum grain sizes up to 200 μm. We calculated the ratio between radiative and gravitational forces to determine whether radiation pressure can disrupt clouds.Results. We find that radiation pressure acting on dust almost never disrupts star-forming clouds. Ultraviolet and optical photons from young stars to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by the dust at thermal wavelengths. As the cloud is typically optically thin to far-infrared radiation, it promptly escapes, depositing little momentum in the cloud. The resulting spectrum is more narrowly peaked than the corresponding Planck function, and exhibits an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm wavelength regime, the resulting radiative force is even smaller than for the corresponding single-temperature blackbody. We find that the force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or moderate starbust conditions. Only for unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity.Conclusions. We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star-formation process on either local or global scales.

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