Second-Generation Objects in the Universe: Radiative Cooling and Collapse of Halos with Virial Temperatures above 104 K

By S. Oh, Zoltán Haiman. 2001

307 citations recorded by the source corpus.

The first generation of stars is thought to have formed in low-mass halos with Tvir < 104 K where H2 cooling is paramount. However, the efficiency of H2 formation and cooling in these halos may have been severely limited by feedback processes. In this paper we investigate the radiative cooling and collapse of halos with virial temperatures Tvir > 104 K, i.e., those that can cool in the absence of H2 via neutral atomic lines. The evolution of these halos differs from their less massive counterparts. Efficient atomic line radiation allows rapid cooling to ~8000 K; subsequently the gas can contract nearly isothermally at this temperature. In the absence of H2 molecules, the gas would likely settle into a locally stable disk, and only disks with unusually low spin would be unstable. However, we find that the initial atomic line cooling leaves a large, out-of-equilibrium residual free electron fraction. This allows the molecular fraction to build up to a universal value of x ≈ 10-3, almost independently of initial density and temperature. We show that this is a nonequilibrium freeze-out value that can be understood in terms of timescale arguments. Unlike in less massive halos, H2 formation and cooling is largely impervious to feedback from external UV fields, due to the high initial densities achieved by atomic cooling. The newly formed molecules cool the gas further to ~100 K and allow the gas to fragment on scales of a few times 100 M☉. We investigate the importance of various feedback effects such as H2 photodissociation from internal UV fields and radiation pressure due to Lyα photon trapping, which are likely to regulate the efficiency of star formation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cac41f7006d435188f20876dee71ae615423e456

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

FORMATION OF THE FIRST NUCLEAR CLUSTERS AND MASSIVE BLACK HOLES AT HIGH REDSHIFT (2008, background): “Disk formation and mass inflow We describe the early evolution of the cooling and collapsing baryons in a simple way, assuming adiabatic response of the halo to gas cooling and disk formation (e.g., Mo, Mao & White 1998, Oh & Haiman 2002, Lodato & Natarajan 2006).”
Fossil H ii regions: self-limiting star formation at high redshift (2003, background): “We can conservatively take into account the H2 enhancement by assuming the maximum initial abundance of H2, xH2 ∼ 10−3; this hard upper limit is independent of density or ionization fraction and is due to ’freeze–out’ c© 0000 RAS, MNRAS 000, 000–000 (Oh & Haiman (2002), hereafter OH02).”
Quasars at z = 6: The Survival of the Fittest (2006, background): “Following Oh & Haiman (2002), we assume that a fraction fd of the gas settles into an isothermal, exponential disc, embedded in a dark matter halo described by a Navarro et al. (1997) density profile.”
Black hole formation in the early Universe (2013, background): “Protogalactic metal free haloes may directly collapse to form SMBHs provided that the fragmentation in these haloes remains suppressed (Oh & Haiman 2002; Bromm & Loeb 2003; Begelman, Volonteri & Rees 2006; Spaans & Silk 2006; Dijkstra et al. 2008; Djorgovski et al. 2008; Schleicher, Spaans & Glover…”
The First Stars (2012, background): “The effects of Lyman-α radiation pressure in metal-free gas were considered by Oh & Haiman (2002), in the context of the formation of massive star-forming minihalos with virial temperatures T > 104 K.”
THE ASSEMBLY OF SUPERMASSIVE BLACK HOLES AT HIGH REDSHIFTS (2008, background): “In most halos whose virial temperature is above 104 K, this assumption is less justified, and a disk may form at the core of the DM halo (Oh & Haiman 2002).”
Suppression of H2 Cooling in the Ultraviolet Background (2007, background): “The photodissociation of H2 via the Solomon process by an early soft ultraviolet background (UVB) is generally assumed as the main reason (Oh & Haiman 2002; Ciardi & Ferrara 2005; Haiman & Bryan 2006).”
Formation of supermassive black holes (2010, background): “A mass M = fd fgasMh would then settle into a rotationally supported disc (Mo et al, 1998; Oh and Haiman, 2002) with a scale radius ' λspinrvir, where rvir is the virial radius of the proto–galaxy.”
Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse (2007, background): “As mass infalls toward the center, the increased cooling rate, which is / nne until Ly radiation becomes trappedwithin the inner condensation at a density of 5 ; 108 cm 3 (Oh & Haiman 2002), catalyzes the collapse as atomic line transitions convert kinetic energy to radiation.”
Supermassive black hole formation during the assembly of pre-galactic discs (2006, methodology): “We consider next the situation wherein molecular hydrogen formation is not suppressed and we assume that it can form up to a molecular fraction xH2 = 10 −3 (Oh & Haiman 2002).”
Can Supermassive Black Holes Form in Metal-enriched High-Redshift Protogalaxies? (2008, background): “Oh & Haiman (2002) and Lodato & Natarajan (2006) have also showed that if H2 formation is inhibited, a primordial gas disk is stable to fragmentation and a single massive object is formed in accordance with BL03’s conclusion.”