scholarly journals Calibration of a star formation and feedback model for cosmological simulations with enzo

2020 ◽  
Vol 497 (4) ◽  
pp. 5203-5219
Author(s):  
Boon Kiat Oh ◽  
Britton D Smith ◽  
John A Peacock ◽  
Sadegh Khochfar
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
Simulation Code ◽  
Cosmological Simulations ◽  
Feedback Parameter ◽  
Stellar Feedback ◽  
Feedback Model ◽  
Wide Range ◽  
Halo Masses ◽  
Parameter Values

ABSTRACT We introduce a new methodology for efficiently tuning sub-grid models of star formation and supernovae feedback in cosmological simulations and at the same time understanding their physical implications. Based on a set of 71 zoom simulations of a Milky Way (MW)-sized halo, we explore the feasibility of calibrating a widely used star formation and feedback model in the enzo simulation code. We propose a novel way to match observations, using functional fits to the observed baryon makeup over a wide range of halo masses. The model MW galaxy is calibrated using three parameters: the star formation efficiency (f*), the efficiency of thermal energy from stellar feedback (ϵ), and the region into which feedback is injected (r  and s). We find that changing the amount of feedback energy affects the baryon content most significantly. We then identify two sets of feedback parameter values that are both able to reproduce the baryonic properties for haloes between $10^{10}\, \mathrm{M_\odot }$ and $10^{12}\, \mathrm{M_\odot }$. We can potentially improve the agreement by incorporating more parameters or physics. If we choose to focus on one property at a time, we can obtain a more realistic halo baryon makeup. Contrasting both star formation criteria and the corresponding combination of optimal feedback parameters, we also highlight that feedback effects can be complementary: to match the same baryonic properties, with a relatively higher gas-to-stars conversion efficiency, the feedback strength required is lower, and vice versa. Lastly, we demonstrate that chaotic variance in the code can cause deviations of approximately 10 per cent and 25 per cent in the stellar and baryon mass in simulations evolved from identical initial conditions.

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

2019 ◽  
Vol 487 (1) ◽  
pp. 364-380 ◽  
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.

scholarly journals Formation sites of Population III star formation: The effects of different levels of rotation and turbulence on the fragmentation behaviour of primordial gas

2020 ◽  
Vol 494 (2) ◽  
pp. 1871-1893 ◽  
Author(s):  
Katharina M J Wollenberg ◽  
Simon C O Glover ◽  
Paul C Clark ◽  
Ralf S Klessen
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
Turbulent Energy ◽  
Star Forming ◽  
Wide Range ◽  
Population Iii Stars ◽  
The Individual ◽  
The Masses ◽  
Different Levels ◽  
Population Iii

ABSTRACT We use the moving-mesh code arepo to investigate the effects of different levels of rotation and turbulence on the fragmentation of primordial gas and the formation of Population III stars. We consider nine different combinations of turbulence and rotation and carry out five different realizations of each setup, yielding one of the largest sets of simulations of Population III star formation ever performed. We find that fragmentation in Population III star-forming systems is a highly chaotic process and show that the outcomes of individual realizations of the same initial conditions often vary significantly. However, some general trends are apparent. Increasing the turbulent energy promotes fragmentation, while increasing the rotational energy inhibits fragmentation. Within the ∼1000 yr period that we simulate, runs including turbulence yield flat protostellar mass functions while purely rotational runs show a more top-heavy distribution. The masses of the individual protostars are distributed over a wide range from a few $10^{-3} \, {\rm M_{\odot }}$ to several tens of M⊙. The total mass growth rate of the stellar systems remains high throughout the simulations and depends only weakly on the degree of rotation and turbulence. Mergers between protostars are common, but predictions of the merger fraction are highly sensitive to the criterion used to decide whether two protostars should merge. Previous studies of Population III star formation have often considered only one realization per set of initial conditions. However, our results demonstrate that robust trends can only be reliably identified by considering averages over a larger sample of runs.

scholarly journals Measuring the spectral index of turbulent gas with deep learning from projected density maps

2020 ◽  
Vol 498 (4) ◽  
pp. 5798-5803
Author(s):  
Piero Trevisan ◽  
Mario Pasquato ◽  
Alessandro Ballone ◽  
Michela Mapelli
Keyword(s):  
Deep Learning ◽  
Star Formation ◽  
Spectral Index ◽  
Adaptive Mesh Refinement ◽  
Mean Squared Error ◽  
Initial Conditions ◽  
Star Cluster ◽  
Large Set ◽  
Simulation Code ◽  
Density Maps

ABSTRACT Turbulence plays a key role in star formation in molecular clouds, affecting star cluster primordial properties. As modelling present-day objects hinges on our understanding of their initial conditions, better constraints on turbulence can result in windfalls in Galactic archaeology, star cluster dynamics, and star formation. Observationally, constraining the spectral index of turbulent gas usually involves computing spectra from velocity maps. Here, we suggest that information on the spectral index might be directly inferred from column density maps (possibly obtained by dust emission/absorption) through deep learning. We generate mock density maps from a large set of adaptive mesh refinement turbulent gas simulations using the hydro-simulation code ramses. We train a convolutional neural network (CNN) on the resulting images to predict the turbulence index, optimize hyperparameters in validation and test on a holdout set. Our adopted CNN model achieves a mean squared error of 0.024 in its predictions on our holdout set, over underlying spectral indexes ranging from 3 to 4.5. We also perform robustness tests by applying our model to altered holdout set images, and to images obtained by running simulations at different resolutions. This preliminary result on simulated density maps encourages further developments on real data, where observational biases and other issues need to be taken into account.

scholarly journals Clumpy galaxies in cosmological simulations: the effect of ISM model

2019 ◽  
Vol 488 (3) ◽  
pp. 4400-4412 ◽  
Author(s):  
Shigeki Inoue ◽  
Naoki Yoshida
Keyword(s):  
Star Formation Rate ◽  
Equations Of State ◽  
Initial Conditions ◽  
Formation Rate ◽  
The Other ◽  
Cosmological Simulations ◽  
Stellar Feedback ◽  
Global Properties ◽  
Significant Difference ◽  
Disc Galaxies

ABSTRACT We study influence by models of interstellar medium (ISM) on properties of galaxies in cosmological simulations. We examine three models widely used in previous studies. The ISM models impose different equations of state on dense gas. Using zoom-in simulations, we demonstrate that switching the ISM models can control formation of giant clumps in massive discs at redshifts z ∼ 1–2, while their initial conditions and the other settings such as stellar feedback are unchanged. Thus, not only feedback but ISM models can also be responsible for clumpy morphologies of simulated galaxies. We find, however, that changing the ISM models hardly affects global properties of galaxies, such as the total stellar and gas masses, star formation rate, metallicity, and stellar angular momentum, irrespective of the significant difference of clumpiness; namely the ISM models only change clumpiness of discs. In addition, our approach provides a test to investigate impact by clump formation on the evolution of disc galaxies using the same initial conditions and feedback. We find that clump formation does not significantly alter the properties of galaxies and therefore could not be the causes of starburst or quenching.

scholarly journals Galactic outflow rates in the EAGLE simulations

2020 ◽  
Vol 494 (3) ◽  
pp. 3971-3997 ◽  
Author(s):  
Peter D Mitchell ◽  
Joop Schaye ◽  
Richard G Bower ◽  
Robert A Crain
Keyword(s):  
Galactic Nuclei ◽  
Mass Function ◽  
Mass Loading ◽  
Stellar Feedback ◽  
Galactic Winds ◽  
Wide Range ◽  
The Galaxy ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Halo Masses

ABSTRACT We present measurements of galactic outflow rates from the eagle suite of cosmological simulations. We find that gas is removed from the interstellar medium (ISM) of central galaxies with a dimensionless mass loading factor that scales approximately with circular velocity as $V_{\mathrm{c}}^{-3/2}$ in the low-mass regime where stellar feedback dominates. Feedback from active galactic nuclei causes an upturn in the mass loading for halo masses ${\gt}10^{12} \, \mathrm{M_\odot }$. We find that more gas outflows through the halo virial radius than is removed from the ISM of galaxies, particularly at low redshifts, implying substantial mass loading within the circumgalactic medium. Outflow velocities span a wide range at a given halo mass/redshift, and on average increase positively with redshift and halo mass up to $M_{200} \sim 10^{12} \, \mathrm{M_\odot }$. Outflows exhibit a bimodal flow pattern on circumgalactic scales, aligned with the galactic minor axis. We present a number of like-for-like comparisons to outflow rates from other recent cosmological hydrodynamical simulations, and show that comparing the propagation of galactic winds as a function of radius reveals substantial discrepancies between different models. Relative to some other simulations, eagle favours a scenario for stellar feedback where agreement with the galaxy stellar mass function is achieved by removing smaller amounts of gas from the ISM, but with galactic winds that then propagate and entrain ambient gas out to larger radii.

scholarly journals The Molecular Cloud Lifecycle

2020 ◽  
Vol 216 (4) ◽  
Author(s):  
Mélanie Chevance ◽  
J. M. Diederik Kruijssen ◽  
Enrique Vazquez-Semadeni ◽  
Fumitaka Nakamura ◽  
Ralf Klessen ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Initial Conditions ◽  
Surrounding Medium ◽  
Building Blocks ◽  
Giant Molecular Clouds ◽  
Numerical Work ◽  
Physical Mechanisms ◽  
Stellar Feedback ◽  
Recent Debate

Abstract Giant molecular clouds (GMCs) and their stellar offspring are the building blocks of galaxies. The physical characteristics of GMCs and their evolution are tightly connected to galaxy evolution. The macroscopic properties of the interstellar medium propagate into the properties of GMCs condensing out of it, with correlations between e.g. the galactic and GMC scale gas pressures, surface densities and volume densities. That way, the galactic environment sets the initial conditions for star formation within GMCs. After the onset of massive star formation, stellar feedback from e.g. photoionisation, stellar winds, and supernovae eventually contributes to dispersing the parent cloud, depositing energy, momentum and metals into the surrounding medium, thereby changing the properties of galaxies. This cycling of matter between gas and stars, governed by star formation and feedback, is therefore a major driver of galaxy evolution. Much of the recent debate has focused on the durations of the various evolutionary phases that constitute this cycle in galaxies, and what these can teach us about the physical mechanisms driving the cycle. We review results from observational, theoretical, and numerical work to build a dynamical picture of the evolutionary lifecycle of GMC evolution, star formation, and feedback in galaxies.

Pop III Supernova Feedback on the Formation of the First Galaxies

2019 ◽  
Vol 15 (S341) ◽  
pp. 253-256 ◽  
Author(s):  
Li-Hsin Chen ◽  
Ke-Jung Chen
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Adaptive Mesh ◽  
Building Blocks ◽  
Dark Matter Halos ◽  
First Stars ◽  
Stellar Feedback ◽  
First Galaxies

AbstractModern cosmological simulations suggest that the hierarchical assembly of dark matter halos provided the gravitational wells that allowed the primordial gases to form stars and galaxies inside them. The first galaxies comprised of the first systems of stars gravitationally bound in dark matter halos are naturally recognized as the building blocks of early Universe. To understand the formation of the first galaxies, we use an adaptive mesh refinement (AMR) cosmological code, Enzo to simulate the formation and evolution of the first galaxies. We first model an isolated galaxy by considering much microphysics such as star formation, stellar feedback, and primordial gas cooling. To examine the effect of Pop III stellar feedback to the first galaxy formation, we adjust the initial temperature, density distribution and metallicity distributions by assuming different IMFs of the first stars. Our results suggest that star formation in the first galaxies is sensitive to the initial conditions of Pop III supernovae and their remnants. Our study can help to correlate the populations of the first stars and supernovae to star formation inside these first galaxies which may be soon observed by the (James Webb Space Telescope JWST).

scholarly journals The Resolved Properties of Extragalactic Giant Molecular Clouds

2008 ◽  
Vol 4 (S255) ◽  
pp. 274-277
Author(s):  
Alberto D. Bolatto ◽  
Adam K. Leroy ◽  
Erik Rosolowsky ◽  
Fabian Walter ◽  
Leo Blitz
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Conversion Factor ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Far Infrared ◽  
Infrared Analysis ◽  
Giant Molecular Clouds ◽  
Starting Point ◽  
Wide Range

AbstractGiant molecular clouds (GMCs) are the major reservoirs of molecular gas in galaxies, and the starting point for star formation. As such, their properties play a key role in setting the initial conditions for the formation of stars. We present a comprehensive combined inteferometric/single-dish study of the resolved GMC properties in a number of extragalactic systems, including both normal and dwarf galaxies. We find that the extragalactic GMC properties measured across a wide range of environments, characterized by the Larson relations, are to first order remarkably compatible with those in the Milky Way. Using these data to investigate trends due to galaxy metallicity, we find that: 1) these measurements are not in accord with simple expectations from photoionization-regulated star formation theory; 2) there is no trend in the virial CO-to-H2conversion factor on the spatial scales studied; and 3) there are measurable departures from the Galactic Larson relations in the Small Magellanic Cloud — the object with the lowest metallicity in the sample — where GMCs have velocity dispersions that are too small for their sizes. We will discuss the stability of these clouds in the light of our recent far-infrared analysis of this galaxy, and will contrast the results of the virial and far-infrared studies on the issue of the CO-to-H2conversion factor and what they tell us about the structure of molecular clouds in primitive galaxies.

PREDICTING REGIMES OF INDETERMINATE JUMPS TO RESONANCE BY ASSESSING FRACTAL BOUNDARIES IN CONTROL SPACE

1994 ◽  
Vol 04 (06) ◽  
pp. 1645-1653 ◽  
Author(s):  
MOHAMED S. SOLIMAN
Keyword(s):  
Initial Conditions ◽  
Initial Study ◽  
Control Space ◽  
Electrical Systems ◽  
Wide Range ◽  
Nonlinear Mechanical ◽  
Sensitive Dependence ◽  
Simplified Method ◽  
Local And Global Bifurcations ◽  
Parameter Values

For nonlinear mechanical, structural and electrical systems, it is important to know, over a wide range of parameter values, whether jumps to resonance exist. Since the outcome may often be indeterminate, we have to identify parameters which place bounds on the determinancy of such jumps. Such an analysis is often quite complex since it involves determining both the main local and global bifurcations (the homoclinic and heteroclinic connections that induce a fractal basin structure at the bifurcation) that can lead to an indeterminate jump to resonance. Utilizing the fact that a sensitive dependence on the initial conditions implies a sensitive dependence on parameters, in this paper we propose a simplified method, based on assessing fractal boundaries in control space, that may be used to reveal aspects of indeterminate bifurcational behaviour of the system. Such an analysis which allows us to identify approximate regimes of indeterminate jumps to resonance, may either be used as an initial study for further detailed analysis, or as a simplified engineering approach in the analysis of systems liable to this type of resonant behaviour.

Sign in / Sign up

Export Citation Format

Share Document