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Title: THE FORMATION OF THE FIRST COSMIC STRUCTURES AND THE PHYSICS OF THE z {approx} 20 UNIVERSE

Abstract

We perform a suite of cosmological simulations in the {Lambda}CDM paradigm of the formation of the first structures in the universe prior to astrophysical reheating and reionization (15 {approx}< z < 200). These are the first simulations initialized in a manner that self-consistently accounts for the impact of pressure on the rate of growth of modes, temperature fluctuations in the gas, and the dark matter-baryon supersonic velocity difference. Even with these improvements, these are still difficult times to simulate accurately as the Jeans length of the cold intergalactic gas must be resolved while also capturing a representative sample of the universe. We explore the box size and resolution requirements to meet these competing objectives. Our simulations support the finding of recent studies that the dark matter-baryon velocity difference has a surprisingly large impact on the accretion of gas onto the first star-forming minihalos (which have masses of {approx}10{sup 6} M {sub Sun }). In fact, the halo gas is often significantly downwind of such halos and with lower densities in the simulations in which the baryons have a bulk flow with respect to the dark matter, modulating the formation of the first stars by the local value of this velocitymore » difference. We also show that dynamical friction plays an important role in the nonlinear evolution of the dark matter-baryon differential velocity, acting to erase this velocity difference quickly in overdense gas, as well as sourcing visually apparent bow shocks and Mach cones throughout the universe. We use simulations with both the GADGET and Enzo cosmological codes to test the robustness of these conclusions. The comparison of these codes' simulations also provides a relatively controlled test of these codes themselves, allowing us to quantify some of the tradeoffs between the algorithms. For example, we find that particle coupling in GADGET between the gas and dark matter particles results in spurious growth that mimics nonlinear growth in the matter power spectrum for standard initial setups. This coupling is alleviated by using adaptive gravitational softening for the gas. In a companion paper, we use the simulations presented here to make detailed estimates for the impact of the dark matter-baryon velocity differential on redshifted 21 cm radiation. The initial conditions generator used in this study, CICSASS, can be publicly downloaded.« less

Authors:
;  [1]
  1. Department of Astronomy, University of California, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22086385
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 760; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALGORITHMS; ASTROPHYSICS; BARYONS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COSMOLOGICAL CONSTANT; COSMOLOGICAL MODELS; COSMOLOGY; COUPLING; DENSITY; ENERGY SPECTRA; FLUCTUATIONS; GALAXIES; NONLINEAR PROBLEMS; NONLUMINOUS MATTER; RED SHIFT; SHOCK WAVES; STARS; UNIVERSE; VELOCITY

Citation Formats

O'Leary, Ryan M, and McQuinn, Matthew. THE FORMATION OF THE FIRST COSMIC STRUCTURES AND THE PHYSICS OF THE z {approx} 20 UNIVERSE. United States: N. p., 2012. Web. doi:10.1088/0004-637X/760/1/4.
O'Leary, Ryan M, & McQuinn, Matthew. THE FORMATION OF THE FIRST COSMIC STRUCTURES AND THE PHYSICS OF THE z {approx} 20 UNIVERSE. United States. https://doi.org/10.1088/0004-637X/760/1/4
O'Leary, Ryan M, and McQuinn, Matthew. Tue . "THE FORMATION OF THE FIRST COSMIC STRUCTURES AND THE PHYSICS OF THE z {approx} 20 UNIVERSE". United States. https://doi.org/10.1088/0004-637X/760/1/4.
@article{osti_22086385,
title = {THE FORMATION OF THE FIRST COSMIC STRUCTURES AND THE PHYSICS OF THE z {approx} 20 UNIVERSE},
author = {O'Leary, Ryan M and McQuinn, Matthew},
abstractNote = {We perform a suite of cosmological simulations in the {Lambda}CDM paradigm of the formation of the first structures in the universe prior to astrophysical reheating and reionization (15 {approx}< z < 200). These are the first simulations initialized in a manner that self-consistently accounts for the impact of pressure on the rate of growth of modes, temperature fluctuations in the gas, and the dark matter-baryon supersonic velocity difference. Even with these improvements, these are still difficult times to simulate accurately as the Jeans length of the cold intergalactic gas must be resolved while also capturing a representative sample of the universe. We explore the box size and resolution requirements to meet these competing objectives. Our simulations support the finding of recent studies that the dark matter-baryon velocity difference has a surprisingly large impact on the accretion of gas onto the first star-forming minihalos (which have masses of {approx}10{sup 6} M {sub Sun }). In fact, the halo gas is often significantly downwind of such halos and with lower densities in the simulations in which the baryons have a bulk flow with respect to the dark matter, modulating the formation of the first stars by the local value of this velocity difference. We also show that dynamical friction plays an important role in the nonlinear evolution of the dark matter-baryon differential velocity, acting to erase this velocity difference quickly in overdense gas, as well as sourcing visually apparent bow shocks and Mach cones throughout the universe. We use simulations with both the GADGET and Enzo cosmological codes to test the robustness of these conclusions. The comparison of these codes' simulations also provides a relatively controlled test of these codes themselves, allowing us to quantify some of the tradeoffs between the algorithms. For example, we find that particle coupling in GADGET between the gas and dark matter particles results in spurious growth that mimics nonlinear growth in the matter power spectrum for standard initial setups. This coupling is alleviated by using adaptive gravitational softening for the gas. In a companion paper, we use the simulations presented here to make detailed estimates for the impact of the dark matter-baryon velocity differential on redshifted 21 cm radiation. The initial conditions generator used in this study, CICSASS, can be publicly downloaded.},
doi = {10.1088/0004-637X/760/1/4},
url = {https://www.osti.gov/biblio/22086385}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 760,
place = {United States},
year = {2012},
month = {11}
}