scholarly journals The FRIGG project: From intermediate galactic scales to self-gravitating cores

2018 ◽  
Vol 611 ◽  
pp. A24 ◽  
Author(s):  
Patrick Hennebelle
Keyword(s):  
Initial Conditions ◽  
Critical Mass ◽  
Adaptive Mesh ◽  
Direct Consequence ◽  
Small Scale ◽  
Core Mass ◽  
Numerical Resolution ◽  
The Core ◽  
Prestellar Cores ◽  
Hydrodynamical Simulations

Context. Understanding the detailed structure of the interstellar gas is essential for our knowledge of the star formation process.Aim. The small-scale structure of the interstellar medium (ISM) is a direct consequence of the galactic scales and making the link between the two is essential.Methods. We perform adaptive mesh simulations that aim to bridge the gap between the intermediate galactic scales and the self-gravitating prestellar cores. For this purpose we use stratified supernova regulated ISM magneto-hydrodynamical simulations at the kpc scale to set up the initial conditions. We then zoom, performing a series of concentric uniform refinement and then refining on the Jeans length for the last levels. This allows us to reach a spatial resolution of a few 10−3 pc. The cores are identified using a clump finder and various criteria based on virial analysis. Their most relevant properties are computed and, due to the large number of objects formed in the simulations, reliable statistics are obtained.Results. The cores’ properties show encouraging agreements with observations. The mass spectrum presents a clear powerlaw at high masses with an exponent close to ≃−1.3 and a peak at about 1–2 M⊙. The velocity dispersion and the angular momentum distributions are respectively a few times the local sound speed and a few 10−2 pc km s−1. We also find that the distribution of thermally supercritical cores present a range of magnetic mass-to-flux over critical mass-to-flux ratios, typically between ≃0.3 and 3 indicating that they are significantly magnetized. Investigating the time and spatial dependence of these statistical properties, we conclude that they are not significantly affected by the zooming procedure and that they do not present very large fluctuations. The most severe issue appears to be the dependence on the numerical resolution of the core mass function (CMF). While the core definition process may possibly introduce some biases, the peak tends to shift to smaller values when the resolution improves.Conclusions. Our simulations, which use self-consistently generated initial conditions at the kpc scale, produce a large number of prestellar cores from which reliable statistics can be inferred. Preliminary comparisons with observations show encouraging agreements. In particular the inferred CMFs resemble the ones inferred from recent observations. We stress, however, a possible issue with the peak position shifting with numerical resolution.

Prestellar Core Collisions - Impact on the formation of the CMF? A case study on FeSt 1-457

2018 ◽  
Vol 14 (S345) ◽  
pp. 328-329
Author(s):  
Gabor I. Herbst-Kiss ◽  
Joao Alves
Keyword(s):  
Molecular Cloud ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Core Mass ◽  
Preliminary Results ◽  
The Core ◽  
Prestellar Cores

AbstractThe initial mass function (IMF) is a profoundly studied subject, however its origin is still unclear and heavily disputed. The Core Mass Function (CMF) has a remarkable resemblance to a shifted IMF along the mass axis of a factor of 3. This CMF has been observed amongst others in the Pipe Nebula, a calm molecular cloud at approximately 130 pc. We study the origin of the CMF under the assumption that collisions and merging of prestellar cores shape the CMF. We present our preliminary results of core collisions for the well known FeSt 1-457.

scholarly journals Models of Type II Supernova Explosions

1986 ◽  
Vol 7 ◽  
pp. 629-633
Author(s):  
Wolfgang Hillebrandt
Keyword(s):  
Main Sequence ◽  
Critical Mass ◽  
Iron Core ◽  
Heavy Nuclei ◽  
Core Mass ◽  
The Core ◽  
Supernova Explosions ◽  
M Stars ◽  
Chandrasekhar Limit ◽  
Carbon Burning

Present stellar evolution codes predict that stars with He-core masses above approximately 2 M⊙, corresponding to main sequence masses of at least 8 M⊙ burn carbon non-violently. After hydrostatic core carbon burning all those stars contain O-Ne-Mg cores but their further evolution is strongly dependent on the stellar entropy and thus on the main sequence and the core mass. If the He-core mass is below 3 M⊙ the O-Ne-Mg core grows due to carbon-burning in a shell and the crucial question is, whether or not it grows beyond the critical mass for Neignition (≅1.37 M⊙). Stars with He-cores less massive than about 2.4 M⊙ will never ignite Ne, but due to electron-captures, mainly on Ne and Mg, their cores will contract until O-burning begins. Since the matter of the O-Ne-Mg core is weakly degenerate O-burning propagates as a (subsonic) deflagration front and incinerates a certain fraction of the core into a nuclear statistical equilibrium (NSE) composition of iron-group elements (Nomoto, 1984). If, on the other hand, the mass of the O-Ne-Mg core is slightly larger than 1.37 M⊙ Ne and O burn in a shell from about 0.6 M⊙ to 1.4 M⊙, but again the outcome is a NSE-composition (Wilson et al., 1985). In both cases the core-mass finally exceeds the Chandrasekhar limit because electron captures on free protons and heavy nuclei lower the electron concentration and consequently also the effective Chandrasekhar mass. The cores, therefore, continue to contract and finally collapse to neutron star densities with iron-core masses between 0.7 and 1.4 M⊙.

scholarly journals Evolution of stars just below the critical mass for iron core formation

2011 ◽  
Vol 7 (S279) ◽  
pp. 407-408
Author(s):  
Koh Takahashi ◽  
Hideyuki Umeda ◽  
Takashi Yoshida
Keyword(s):  
Production Rate ◽  
Electron Capture ◽  
Energy Production ◽  
Critical Mass ◽  
Initial Mass ◽  
Iron Core ◽  
Core Formation ◽  
Core Mass ◽  
Core Electron ◽  
The Core

AbstractWe calculate the evolution of stars with their initial mass of 9-11M⊙ under very fine initial mass grid of 0.01M⊙. We determine the lower critical mass for Ne ignition in an ONe core that has not undergone the thermal pulse episode. The values are 9.83M⊙ for the initial mass and 1.365M⊙ for the CO core mass. A star with an initial mass slightly larger than the critical, undergoes an off-center Ne+O ignition. Since the energy production rate of Ne+O burning and lasting electron capture reactions is sufficiently large to ignite Si, an Fe core forms as a result of shell Si burning. For a star just below the critical mass, an ONe core continues to contract. In such a high density core, electron capture by nuclei produced through C burning affects the core evolution. After 20Ne starts to capture electrons, the core may ignite O and undergo O detonation. The fate may be an Electron Capture Supernova.

H 2 , H 3 + and the age of molecular clouds and prestellar cores

2012 ◽  
Vol 370 (1978) ◽  
pp. 5200-5212 ◽  
Author(s):  
L. Pagani ◽  
P. Lesaffre ◽  
E. Roueff ◽  
M. Jorfi ◽  
P. Honvault ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Initial Conditions ◽  
Molecular Gas ◽  
New Approach ◽  
The Core ◽  
Dense Cores ◽  
Prestellar Cores ◽  
Deuterium Enrichment ◽  
Abundance And Distribution ◽  
Static Core

Measuring the age of molecular clouds and prestellar cores is a difficult task that has not yet been successfully accomplished although the information is of paramount importance to help in understanding and discriminating between different formation scenarios. Most chemical clocks suffer from unknown initial conditions and are therefore difficult to use. We propose a new approach based on a subset of deuterium chemistry that takes place in the gas phase and for which initial conditions are relatively well known. It relies primarily on the conversion of H 3 + into H 2 D + to initiate deuterium enrichment of the molecular gas. This conversion is controlled by the ortho/para ratio of H 2 that is thought to be produced with the statistical ratio of 3 and subsequently slowly decays to an almost pure para-H 2 phase. This slow decay takes approximately 1 Myr and allows us to set an upper limit on the age of molecular clouds. The deuterium enrichment of the core takes longer to reach equilibrium and allows us to estimate the time necessary to form a dense prestellar core, i.e. the last step before the collapse of the core into a protostar. We find that the observed abundance and distribution of DCO + and N 2 D + argue against quasi-static core formation and favour dynamical formation on time scales of less than 1 Myr. Another consequence is that ortho-H 2 remains comparable to para-H 2 in abundance outside the dense cores.

scholarly journals What determines the formation and characteristics of protoplanetary discs?

2020 ◽  
Vol 635 ◽  
pp. A67 ◽  
Author(s):  
Patrick Hennebelle ◽  
Benoit Commerçon ◽  
Yueh-Ning Lee ◽  
Sébastien Charnoz
Keyword(s):  
Adaptive Mesh Refinement ◽  
Initial Conditions ◽  
Adaptive Mesh ◽  
Small Scale ◽  
Initial Structure ◽  
Solar Mass ◽  
Central Object ◽  
The Impact ◽  
Protoplanetary Discs

Context. Planets form in protoplanetary discs. Their masses, distribution, and orbits sensitively depend on the structure of the protoplanetary discs. However, what sets the initial structure of the discs in terms of mass, radius and accretion rate is still unknown. Aims. It is therefore of great importance to understand exactly how protoplanetary discs form and what determines their physical properties. We aim to quantify the role of the initial dense core magnetisation, rotation, turbulence, and misalignment between rotation and magnetic field axis as well as the role of the accretion scheme onto the central object. Methods. We performed non-ideal magnetohydrodynamics numerical simulations using the adaptive mesh refinement code Ramses of a collapsing, one solar mass molecular core to study the disc formation and early, up to 100 kyr, evolution. We paid particular attention to the impact of numerical resolution and accretion scheme. Results. We found that the mass of the central object is almost independent of the numerical parameters such as the resolution and the accretion scheme onto the sink particle. The disc mass and to a lower extent its size, however heavily depend on the accretion scheme, which we found is itself resolution dependent. This implies that the accretion onto the star and through the disc are largely decoupled. For a relatively large domain of initial conditions (except at low magnetisation), we found that the properties of the disc do not change too significantly. In particular both the level of initial rotation and turbulence do not influence the disc properties provide the core is sufficiently magnetised. After a short relaxation phase, the disc settles in a stationary state. It then slowly grows in size but not in mass. The disc itself is weakly magnetised but its immediate surrounding on the contrary is highly magnetised. Conclusions. Our results show that the disc properties directly depend on the inner boundary condition, i.e. the accretion scheme onto the central object. This suggests that the disc mass is eventually controlled by a small-scale accretion process, possibly the star-disc interaction. Because of ambipolar diffusion and its significant resistivity, the disc diversity remains limited and except for low magnetisation, their properties are weakly sensitive to initial conditions such as rotation and turbulence.

scholarly journals Distortion of magnetic fields in Barnard 68

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Ryo Kandori ◽  
Motohide Tamura ◽  
Masao Saito ◽  
Kohji Tomisaka ◽  
Tomoaki Matsumoto ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Critical Mass ◽  
Polarized Light ◽  
Evolutionary Status ◽  
Core Mass ◽  
The Core ◽  
Magnetic Field Modeling ◽  
Inclination Angles

Abstract The magnetic field structure, kinematical stability, and evolutionary status of the starless dense core Barnard 68 (B68) are revealed based on the near-infrared polarimetric observations of background stars, measuring the dichroically polarized light produced by aligned dust grains in the core. After subtracting unrelated ambient polarization components, the magnetic fields pervading B68 are mapped using 38 stars and axisymmetrically distorted hourglass-like magnetic fields are obtained, although the evidence for the hourglass field is not very strong. On the basis of simple 2D and 3D magnetic field modeling, the magnetic inclination angles on the plane-of-sky and in the line-of-sight direction are determined to be 47° ± 5° and 20° ± 10°, respectively. The total magnetic field strength of B68 is obtained to be $26.1 \pm 8.7\, \mu \mbox{G}$. The critical mass of B68, evaluated using both magnetic and thermal/turbulent support, is $M_{\rm cr} = 2.30 \pm 0.20\, {M}_{\odot }$, which is consistent with the observed core mass of $M_{\rm core}=2.1\, M_{\odot }$, suggesting a nearly critical state. We found a relatively linear relationship between polarization and extinction up to AV ∼ 30 mag toward the stars with deepest obscuration. Further theoretical and observational studies are required to explain the dust alignment in cold and dense regions in the core.

scholarly journals Physical properties and chemical composition of the cores in the California molecular cloud

2018 ◽  
Vol 620 ◽  
pp. A163 ◽  
Author(s):  
Guo-Yin Zhang ◽  
Jin-Long Xu ◽  
A. I. Vasyunin ◽  
D. A. Semenov ◽  
Jun-Jie Wang ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Composition ◽  
Physical Properties ◽  
Molecular Cloud ◽  
Initial Conditions ◽  
Mass Function ◽  
High Mass ◽  
Core Mass ◽  
Prestellar Cores ◽  
Formation Efficiency

Aims. We aim to reveal the physical properties and chemical composition of the cores in the California molecular cloud (CMC), so as to better understand the initial conditions of star formation. Methods. We made a high-resolution column density map (18.2′′) with Herschel data, and extracted a complete sample of the cores in the CMC with the fellwalker algorithm. We performed new single-pointing observations of molecular lines near 90 GHz with the IRAM 30m telescope along the main filament of the CMC. In addition, we also performed a numerical modeling of chemical evolution for the cores under the physical conditions. Results. We extracted 300 cores, of which 33 are protostellar and 267 are starless cores. About 51% (137 of 267) of the starless cores are prestellar cores. Three cores have the potential to evolve into high-mass stars. The prestellar core mass function (CMF) can be well fit by a log-normal form. The high-mass end of the prestellar CMF shows a power-law form with an index α = −0.9 ± 0.1 that is shallower than that of the Galactic field stellar mass function. Combining the mass transformation efficiency (ε) from the prestellar core to the star of 15 ± 1% and the core formation efficiency (CFE) of 5.5%, we suggest an overall star formation efficiency of about 1% in the CMC. In the single-pointing observations with the IRAM 30m telescope, we find that 6 cores show blue-skewed profile, while 4 cores show red-skewed profile. [HCO+]/[HNC] and [HCO+]/[N2H+] in protostellar cores are higher than those in prestellar cores; this can be used as chemical clocks. The best-fit chemical age of the cores with line observations is ~5 × 104 yr.

scholarly journals A deep learning approach to test the small-scale galaxy morphology and its relationship with star formation activity in hydrodynamical simulations

2020 ◽  
Author(s):  
Lorenzo Zanisi ◽  
Marc Huertas-Company ◽  
François Lanusse ◽  
Connor Bottrell ◽  
Annalisa Pillepich ◽  
...  
Keyword(s):  
Deep Learning ◽  
Galaxy Formation ◽  
Morphological Structure ◽  
Sloan Digital Sky Survey ◽  
Small Scale ◽  
Learning Approach ◽  
Numerical Resolution ◽  
Star Formation Activity ◽  
Unsupervised Deep Learning ◽  
Hydrodynamical Simulations

Abstract Hydrodynamical simulations of galaxy formation and evolution attempt to fully model the physics that shapes galaxies. The agreement between the morphology of simulated and real galaxies, and the way the morphological types are distributed across galaxy scaling relations are important probes of our knowledge of galaxy formation physics. Here we propose an unsupervised deep learning approach to perform a stringent test of the fine morphological structure of galaxies coming from the Illustris and IllustrisTNG (TNG100 and TNG50) simulations against observations from a subsample of the Sloan Digital Sky Survey. Our framework is based on PixelCNN, an autoregressive model for image generation with an explicit likelihood. We adopt a strategy that combines the output of two PixelCNN networks in a metric that isolates the small-scale morphological details of galaxies from the sky background. We are able to quantitatively identify the improvements of IllustrisTNG, particularly in the high-resolution TNG50 run, over the original Illustris. However, we find that the fine details of galaxy structure are still different between observed and simulated galaxies. This difference is mostly driven by small, more spheroidal, and quenched galaxies which are globally less accurate regardless of resolution and which have experienced little improvement between the three simulations explored. We speculate that this disagreement, that is less severe for quenched disky galaxies, may stem from a still too coarse numerical resolution, which struggles to properly capture the inner, dense regions of quenched spheroidal galaxies.

scholarly journals Is there enough star formation in simulated protoclusters?

2020 ◽  
Vol 501 (2) ◽  
pp. 1803-1822
Author(s):  
Seunghwan Lim ◽  
Douglas Scott ◽  
Arif Babul ◽  
David J Barnes ◽  
Scott T Kay ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Star Formation History ◽  
Test Case ◽  
Numerical Resolution ◽  
Formation History ◽  
Order Of Magnitude ◽  
History Of ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT As progenitors of the most massive objects, protoclusters are key to tracing the evolution and star formation history of the Universe, and are responsible for ${\gtrsim }\, 20$ per cent of the cosmic star formation at $z\, {\gt }\, 2$. Using a combination of state-of-the-art hydrodynamical simulations and empirical models, we show that current galaxy formation models do not produce enough star formation in protoclusters to match observations. We find that the star formation rates (SFRs) predicted from the models are an order of magnitude lower than what is seen in observations, despite the relatively good agreement found for their mass-accretion histories, specifically that they lie on an evolutionary path to become Coma-like clusters at $z\, {\simeq }\, 0$. Using a well-studied protocluster core at $z\, {=}\, 4.3$ as a test case, we find that star formation efficiency of protocluster galaxies is higher than predicted by the models. We show that a large part of the discrepancy can be attributed to a dependence of SFR on the numerical resolution of the simulations, with a roughly factor of 3 drop in SFR when the spatial resolution decreases by a factor of 4. We also present predictions up to $z\, {\simeq }\, 7$. Compared to lower redshifts, we find that centrals (the most massive member galaxies) are more distinct from the other galaxies, while protocluster galaxies are less distinct from field galaxies. All these results suggest that, as a rare and extreme population at high z, protoclusters can help constrain galaxy formation models tuned to match the average population at $z\, {\simeq }\, 0$.

scholarly journals The anisotropy of the power spectrum in periodic cosmological simulations

2021 ◽  
Vol 503 (4) ◽  
pp. 5638-5645
Author(s):  
Gábor Rácz ◽  
István Szapudi ◽  
István Csabai ◽  
László Dobos
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Power Spectra ◽  
Cosmological Simulations ◽  
Spherical Collapse ◽  
Lower Amplitude ◽  
Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

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