Simulations of Early Structure Formation: Primordial Gas Clouds

By Naoki Yoshida, Tom Abel, L. Hernquist, N. Sugiyama. 2003

453 citations recorded by the source corpus.

We use cosmological simulations to study the origin of primordial star-forming clouds in a ΛCDM universe, by following the formation of dark matter halos and the cooling of gas within them. To model the physics of chemically pristine gas, we employ a nonequilibrium treatment of the chemistry of nine species (e−, H, H+, He, He+, He++, H2, H, H−) and include cooling by molecular hydrogen. By considering cosmological volumes, we are able to study the statistical properties of primordial halos, and the high resolution of our simulations enables us to examine these objects in detail. In particular, we explore the hierarchical growth of bound structures forming at redshifts z ≈ 25-30 with total masses in the range ≈105-106 M☉. We find that when the amount of molecular hydrogen in these objects reaches a critical level, cooling by rotational line emission is efficient, and dense clumps of cold gas form. We identify these "gas clouds" as sites for primordial star formation. In our simulations, the threshold for gas cloud formation by molecular cooling corresponds to a critical halo mass of ≈5 × 105 h-1 M☉, in agreement with earlier estimates, but with a weak dependence on redshift in the range z > 16. The complex interplay between the gravitational formation of dark halos and the thermodynamic and chemical evolution of the gas clouds compromises analytic estimates of the critical H2 fraction. Dynamical heating from mass accretion and mergers opposes relatively inefficient cooling by molecular hydrogen, delaying the production of star-forming clouds in rapidly growing halos. We also investigate the effect of photodissociating ultraviolet radiation on the formation of primordial gas clouds. We consider two extreme cases, first by including a uniform radiation field in the optically thin limit and second by accounting for the maximum effect of gas self-shielding in virialized regions. For radiation with Lyman-Werner band flux J > 10-23 ergs s-1 cm-2 Hz-1 sr-1, hydrogen molecules are rapidly dissociated, rendering gas cooling inefficient. In both the cases we consider, the overall effect can be described by computing an equilibrium H2 abundance for the radiation flux and defining an effective shielding factor. Based on our numerical results, we develop a semianalytic model of the formation of the first stars and demonstrate how it can be coupled with large N-body simulations to predict the star formation rate in the early universe.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c3063c670e098d34cde34d9fe5b455b0ffa56750

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In Astronomy and Astrophysics

1. L. Hernquist
2. Volker Springel
3. P. Hopkins
4. Volker Bromm
5. Tom Abel
6. S. Glover
7. John H. Wise
8. A. Ferrara

Citations in the corpus

• Formation of Supermassive Black Hole Seeds (2016, background): “The latter studies also showed that Pop III stars were born in isolation with typical mass accretion rates of 10−4 − 10−2 M⊙/yr (Yoshida et al. 2003, 2006; O’Shea & Norman 2007; Yoshida et al. 2008).”
• Population III Star Formation in a ΛCDM Universe. II. Effects of a Photodissociating Background (2007, methodology): “We note that highest value considered by Machacek et al. (2001) was J21 ¼ 0:0796, and the highest simulated by Yoshida et al. (2003) was J21 ¼ 0:1.”
• Charting the parameter space of the global 21-cm signal (2016, background): “…dominate: (1) radiative cooling of molecular hydrogen happens in the smallest halos, with mass above 105 M⊙ (e.g., Tegmark et al. 1997; Bromm et al. 2002; Yoshida et al. 2003), and (2) radiative cooling of atomic hydrogen takes place in halos with mass above 107 M⊙ (e.g., Barkana & Loeb 2001).”
• The first galaxies : assembly, cooling and the onset of turbulence (2008, background): “Better agreement could be expected if one accounted for the fluctuation power on scales greater than the computational box (see Yoshida et al. 2003).”
• The aftermath of the first stars: massive black holes (2006, background): “This may indeed be the case in regions near the first stars where the LW flux generated during their <∼ 3 Myr lives could destroy the H2 molecules inside the pre-collapse haloes, depriving them of the coolants that allow for star formation (e.g. Yoshida et al. 2003).”
• FORMATION OF MASSIVE PRIMORDIAL STARS: INTERMITTENT UV FEEDBACK WITH EPISODIC MASS ACCRETION (2015, background): “The formation of such massive primordial stars is thought to begin in mini-haloes at z ' 20 − 30 (e.g., Abel et al. 2002; Yoshida et al. 2003), forming tiny embryo protostars (M∗ ∼ 10−2 M ) after the gravitational collapse of natal clouds (e.g., Omukai & Nishi 1998; Yoshida et al. 2008).”
• The First Stars (2012, background): “This phenomenon was noted by Yoshida et al. (2003) in their cosmological simulations of the formation of the first star-forming minihalos.”
• Photodissociation of H2 in protogalaxies: modelling self‐shielding in three‐dimensional simulations (2011, methodology): “The “Six–Ray Approximation” Finally we consider one non–local method, variations of which have been implemented in simulations by, e.g., Yoshida et al. (2003, 2007) and Glover & Mac Low (2007a,b).”
• THE SPECTRAL EVOLUTION OF THE FIRST GALAXIES. I. JAMES WEBB SPACE TELESCOPE DETECTION LIMITS AND COLOR CRITERIA FOR POPULATION III GALAXIES (2011, background): “…III stars are expected to form in isolation or in small numbers within ∼105– 106M⊙ dark matter halos at redshifts z ≈ 20–50 (e.g. Tegmark et al. 1997; Yoshida et al. 2003), but the prospects of detecting such stars on an individual basis appear bleak (e.g. Gardner et al. 2006; Greif et al.…”
• The distribution and kinematics of early high-σ peaks in present-day haloes: implications for rare objects and old stellar populations (2005, background): “…stars may have formed out of metal-free gas in dark matter minihaloes of mass above 6 × 105 M (Abel, Bryan & Norman 2000; Bromm, Coppi & Larson 2002; Yoshida et al. 2003; Kuhlen & Madau 2005) condensing from rare high-σ peaks of the primordial density fluctuation field at z > 20, and were…”
• The First Stars: Mass Growth Under Protostellar Feedback (2011, background): “These stars are thought to have formed around z & 20 within minihaloes of mass M ∼ 106 M⊙, when the dark matter (DM) potential well of the minihalo becomes large enough to gather in primordial gas (e.g. Haiman et al. 1996; Tegmark et al. 1997; Yoshida et al. 2003).”
• 21 Centimeter Fluctuations from Cosmic Gas at High Redshifts (2003, background): “The timing, morphology, and duration of this event contain a wealth of information about both the ionizing sources and the IGM (e.g., Wyithe & Loeb 2003; Cen 2003; Haiman & Holder 2003; Mackey et al. 2003; Yoshida et al. 2003a,d).”
• Resolving the Formation of Protogalaxies. I. Virialization (2007, result): “Similar results have been reported in cosmological simulations of collapses of the first stars (Abel et al. 2000, 2002; Yoshida et al. 2003, 2006b; O’Shea & Norman 2007).”
• Early Reionization by Miniquasars (2003, background): “In popular cold dark matter (CDM) hierarchical cosmogonies, the very first generation of metal-free (‘Population III’) stars is expected to form in dark matter ‘minihalos’ of total mass Mh ∼> 5× 105M⊙ (e.g. Fuller & Couchman 2000; Yoshida et al. 2003) condensing due to H2 cooling from the high-σ pea”
• Two populations of metal-free stars in the early Universe (2006, methodology): “Such minihaloes have virial temperatures in excess of a minimum value, Tmin ≃ 10 3 K, required for collapsing gas to cool in less than a Hubble time (e.g. Haiman et al. 1996; Tegmark et al. 1997, Yoshida et al. 2003).”
• Probing the cosmic reionization history and local environment of gamma‐ray bursts through radio dispersion (2003, methodology): “This may possibly be consistent with numerical simulation results of primordial galaxy formation which sometimes reveal disk-like structures with densities n ∼ 103 − 104cm−3 at z ∼ 20 (Abel, Bryan & Norman 2002, Bromm, Coppi & Larson 2002, Yoshida et al. 2003).”
• Uncertainties in H2 and HD chemistry and cooling and their role in early structure formation (2008, background): “Moreover, previous work by Yoshida et al. (2003) has shown that variations in the cooling time of the gas at low densities can have a pronounced effect on the supply of cold gas available for Population III star formation, and on the timing of the collapse.”