scholarly journals The importance of initial conditions and metallicity for the fragmentation of protogalactic gas

2009 ◽  
Vol 5 (S265) ◽  
pp. 65-66
Author(s):  
Anne-Katharina Jappsen ◽  
Simon C. O. Glover ◽  
Mordecai-Mark Mac Low ◽  
Ralf S. Klessen
Keyword(s):  
Initial Conditions ◽  
Three Dimensional ◽  
Mass Function ◽  
Initial Mass Function ◽  
Ionized Gas ◽  
First Stars ◽  
Particle Hydrodynamics ◽  
Order Of Magnitude ◽  
Smoothed Particle ◽  
Metal Abundances

AbstractThe formation of the first stars out of metal-free gas appears to result in stars at least an order of magnitude more massive than in the present-day case. We here consider what controls the transition from a primordial to a modern initial mass function. We study the influence of low levels of metal enrichment and different initial conditions on the cooling and collapse of initially ionized gas in small protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations. We argue that fragmentation at moderate density depends on the initial conditions for star formation more than on the metal abundances present.

scholarly journals The importance of magnetic fields for the initial mass function of the first stars

2020 ◽  
Vol 497 (1) ◽  
pp. 336-351 ◽  
Author(s):  
Piyush Sharda ◽  
Christoph Federrath ◽  
Mark R Krumholz
Keyword(s):  
Magnetic Fields ◽  
Initial Conditions ◽  
High Redshift ◽  
Three Dimensional ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Dynamo Theory ◽  
First Stars ◽  
High Redshift Galaxies

ABSTRACT Magnetic fields play an important role for the formation of stars in both local and high-redshift galaxies. Recent studies of dynamo amplification in the first dark matter haloes suggest that significant magnetic fields were likely present during the formation of the first stars in the Universe at redshifts of 15 and above. In this work, we study how these magnetic fields potentially impact the initial mass function (IMF) of the first stars. We perform 200 high-resolution, three-dimensional (3D), magnetohydrodynamic (MHD) simulations of the collapse of primordial clouds with different initial turbulent magnetic field strengths as predicted from turbulent dynamo theory in the early Universe, forming more than 1100 first stars in total. We detect a strong statistical signature of suppressed fragmentation in the presence of strong magnetic fields, leading to a dramatic reduction in the number of first stars with masses low enough that they might be expected to survive to the present-day. Additionally, strong fields shift the transition point where stars go from being mostly single to mostly multiple to higher masses. However, irrespective of the field strength, individual simulations are highly chaotic, show different levels of fragmentation and clustering, and the outcome depends on the exact realization of the turbulence in the primordial clouds. While these are still idealized simulations that do not start from cosmological initial conditions, our work shows that magnetic fields play a key role for the primordial IMF, potentially even more so than for the present-day IMF.

scholarly journals Assessing the influence of metallicity on fragmentation of proto-galactic gas

2006 ◽  
Vol 2 (14) ◽  
pp. 268-268
Author(s):  
Anne-Katharina Jappsen ◽  
Simon C. O. Glover ◽  
Ralf S. Klessen ◽  
Mordecai-Mark Mac Low
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Cold Dark Matter ◽  
Three Dimensional ◽  
Metal Enrichment ◽  
Ionized Gas ◽  
First Stars ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Levels ◽  
Do So

AbstractIn cold dark matter cosmological models, the first stars to form are believed to do so within small protogalaxies. We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in these protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations.

scholarly journals Population III.1 stars: formation, feedback and evolution of the IMF

2008 ◽  
Vol 4 (S255) ◽  
pp. 24-32 ◽  
Author(s):  
Jonathan C. Tan
Keyword(s):  
Dark Matter ◽  
Initial Conditions ◽  
Mass Function ◽  
Initial Mass Function ◽  
Dark Matter Annihilation ◽  
Subsequent Evolution ◽  
First Stars ◽  
Field Amplification ◽  
Accretion Rates ◽  
Stars Formation

AbstractI discuss current theoretical expectations of how primordial, Pop III.1 stars form. Lack of direct observational constraints makes this a challenging task. In particular predicting the mass of these stars requires solving a series of problems, which all affect, perhaps drastically, the final outcome. While there is general agreement on the initial conditions, H2-cooled gas at the center of dark matter minihalos, the subsequent evolution is more uncertain. In particular, I describe the potential effects of dark matter annihilation heating, fragmentation within the minihalo, magnetic field amplification, and protostellar ionizing feedback. After these considerations, one expects that the first stars are massive ≳100M⊙, with dark matter annihilation heating having the potential to raise this scale by large factors. Higher accretion rates in later-forming minihalos may cause the Pop III.1 initial mass function to evolve to higher masses.

scholarly journals Do ultracompact dwarf galaxies form monolithically or as merged star cluster complexes?

2021 ◽  
Vol 502 (4) ◽  
pp. 5185-5199
Author(s):  
Hamidreza Mahani ◽  
Akram Hasani Zonoozi ◽  
Hosein Haghi ◽  
Tereza Jeřábková ◽  
Pavel Kroupa ◽  
...  
Keyword(s):  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Mass Function ◽  
Star Cluster ◽  
Initial Mass Function ◽  
Central Mass ◽  
Cluster Complexes ◽  
V Band ◽  
Stellar Masses ◽  
The Imf

ABSTRACT Some ultracompact dwarf galaxies (UCDs) have elevated observed dynamical V-band mass-to-light (M/LV) ratios with respect to what is expected from their stellar populations assuming a canonical initial mass function (IMF). Observations have also revealed the presence of a compact dark object in the centres of several UCDs, having a mass of a few to 15 per cent of the present-day stellar mass of the UCD. This central mass concentration has typically been interpreted as a supermassive black hole, but can in principle also be a subcluster of stellar remnants. We explore the following two formation scenarios of UCDs: (i) monolithic collapse and (ii) mergers of star clusters in cluster complexes as are observed in massively starbursting regions. We explore the physical properties of the UCDs at different evolutionary stages assuming different initial stellar masses of the UCDs and the IMF being either universal or changing systematically with metallicity and density according to the integrated Galactic IMF theory. While the observed elevated M/LV ratios of the UCDs cannot be reproduced if the IMF is invariant and universal, the empirically derived IMF that varies systematically with density and metallicity shows agreement with the observations. Incorporating the UCD-mass-dependent retention fraction of dark remnants improves this agreement. In addition, we apply the results of N-body simulations to young UCDs and show that the same initial conditions describing the observed M/LV ratios reproduce the observed relation between the half-mass radii and the present-day masses of the UCDs. The findings thus suggest that the majority of UCDs that have elevated M/LV ratios could have formed monolithically with significant remnant-mass components that are centrally concentrated, while those with small M/LV values may be merged star cluster complexes.

scholarly journals Turbulent structure and star formation in a stratified, supernova-driven, interstellar medium

2006 ◽  
Vol 2 (S237) ◽  
pp. 358-362
Author(s):  
M. K. Ryan Joung ◽  
Mordecai-Mark Mac Low
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Adaptive Mesh Refinement ◽  
Formation Rate ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Mass Function ◽  
Initial Mass Function ◽  
Interstellar Turbulence ◽  
Self Gravity

AbstractWe report on a study of interstellar turbulence driven by both correlated and isolated supernova explosions. We use three-dimensional hydrodynamic models of a vertically stratified interstellar medium run with the adaptive mesh refinement code Flash at a maximum resolution of 2 pc, with a grid size of 0.5 × 0.5 × 10 kpc. Cold dense clouds form even in the absence of self-gravity due to the collective action of thermal instability and supersonic turbulence. Studying these clouds, we show that it can be misleading to predict physical properties such as the star formation rate or the stellar initial mass function using numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. The amount of mass available for collapse depends on scale, suggesting a simple translation from the density PDF to the stellar IMF may be questionable. Even though the supernova-driven turbulence does produce compressed clouds, it also opposes global collapse. The net effect of supernova-driven turbulence is to inhibit star formation globally by decreasing the amount of mass unstable to gravitational collapse.

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