Suppression of H2 Cooling in the Ultraviolet Background

By John H. Wise, Tom Abel. 2007

137 citations recorded by the source corpus.

The first luminous objects in the concordance cosmology form by molecular hydrogen cooling in dark matter dominated halos of masses ~106 M☉. We use Eulerian adaptive mesh refinement simulations to demonstrate that in the presence of a large soft ultraviolet radiation background, molecular hydrogen is the dominant coolant. Even for very large radiation backgrounds, the halo masses that cool and collapse are up to 2 orders of magnitude smaller than the halos that cool via atomic hydrogen line cooling. The abundance of cooling halos and the cosmic mass fraction contained within them depends exponentially on this critical mass scale. Consequently, the majority of current models of cosmological reionization, chemical evolution, supermassive black hole formation, and galaxy formation underestimate the number of star-forming progenitors of a given system by orders of magnitude. At the highest redshifts, this disagreement is largest. We also show that even in the absence of residual electrons, collisional ionization in central shocks create a sufficient amount of electrons to form molecular hydrogen and cool the gas in halos of virial temperatures far below the atomic cooling limit.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/72435d1ea5d9c845148829e005d9db74eff1cf96

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The birth of a galaxy – III. Propelling reionization with the faintest galaxies (2014, background): “However, previous numerical studies have shown that H2 formation and radiative cooling occurs in lower mass haloes, even in the presence of a strong LW radiation field (Wise & Abel 2007; O’Shea & Norman 2008).”
Galaxy formation theory (2010, background): “…et al. 2008; O’Shea and Norman 2007, 2008; Harris et al. 2007; Stacy and Bromm 2007) may be crucialfor understanding how this population of galaxies grows (Tegmark et al. 1997; Ricotti et al. 2001; Wise and Abel 2007a,b; Greif et al. 2008; Wise and Abel 2008b; Wise et al. 2008; Bromm et al. 2009).”
Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse (2007, background): “We repeat that this isothermal collapse occurs through atomic hydrogen cooling only, but in reality, H2 cooling is important even in the presence of a ultraviolet background (e.g., Machacek et al. 2001; Wise & Abel 2007b; O’Shea & Norman 2008).”
The Destruction of Cosmological Minihalos by Primordial Supernovae (2008, background): “…is yes if one considers halos at slightly later redshifts in rising Lyman-Werner backgrounds, whose effect is to postpone star formation in halos until they reach larger masses and become self-shielded to photodissociating photons (Machacek et al. 2001; O’Shea & Norman 2008; Wise & Abel 2007c).”
Ubiquitous seeding of supermassive black holes by direct collapse (2012, background): “Even a small, uniformJLW ≈ 0.01 from these stars can affect Pop III star forming minihaloes by dissociating a fraction of the H2 molecules and preventing the gas from cooling and collapsing (Machacek et al. 2001; Yoshida et l. 2003; Wise & Abel 2007; O’Shea & Norman 2008).”
FORMATION RATES OF POPULATION III STARS AND CHEMICAL ENRICHMENT OF HALOS DURING THE REIONIZATION ERA (2009, background): “…to numerical simulations: O’Shea & Norman (2008) found in fact that while in the presence of a strong feedback Tvir ≈ 104 K is required for collapse, the cooling is still driven at the center of the halo by molecular hydrogen formed thanks to the high central density (see also Wise & Abel 2007).”
The First Billion Years project: the impact of stellar radiation on the co-evolution of Populations II and III (2012, background): “…are critical for the cooling of the primordial gas, it is expected that their destruction leads to diminished rates of gas collapse and Pop III star formation (e.g. Omukai & Nishi 1999; Machacek et al. 2001; Mesinger et al. 2006a; Wise & Abel 2007; O’Shea & Norman 2008; Trenti et al. 2009).”
The first galaxies : assembly, cooling and the onset of turbulence (2008, background): “Even a single SN from a massive Pop III star would already suffice to reach levels above the critical metallicity, at least on average (Bromm et al. 2003; Greif et al. 2007; Wise & Abel 2007c).”
GALAXY PROPERTIES AND UV ESCAPE FRACTIONS DURING THE EPOCH OF REIONIZATION: RESULTS FROM THE RENAISSANCE SIMULATIONS (2016, background): “LW radiation may significantly delay the Pop III formation in low-mass halos (Machacek et al. 2001; Wise & Abel 2007; O’Shea & Norman 2008), and thus the enrichment history and the emergence of metal-enriched stars in those halos.”
Photodissociation of H2 in protogalaxies: modelling self‐shielding in three‐dimensional simulations (2011, methodology): “…studies have typically either adopted the optically–thin dissociation rate throughout (Machacek et al. 2001, 2003; Mesinger et al. 2006, 2009; Wise & Abel 2007, 2008a,b; Greif et al. 2010), relied upon estimating NH2 from local properties of the gas (Bromm & Loeb 2003; Johnson et al. 2008;…”
A QUANTITATIVE EXPLANATION OF THE OBSERVED POPULATION OF MILKY WAY SATELLITE GALAXIES (2009, background): “…get hot enough to cool by atomic processes, and simulations that include molecular cooling suggest that gas cooling and star formation is very inefficient in such halos (Haiman et al. 1997; Barkana & Loeb 1999; Machacek et al. 2001; Wise & Abel 2007; O’Shea & Norman 2008; Bovill & Ricotti 2008).”
The birth of a galaxy – II. The role of radiation pressure (2012, background): “For example, virial shocks and internal weak shocks have been found to drive turbulence during halo virialization (Wise & Abel 2007a; Greif et al. 2008).”
Supermassive black hole formation by direct collapse: keeping protogalactic gas H2 free in dark matter haloes with virial temperatures Tvir > rsim 104 K (2009, background): “The critical value has been found to be J21 ∼ 0.1 (Haiman et al. 1997; Machacek et al. 2001, 2003; Mesinger et al. 2006, 2008; Wise & Abel 2007; O’Shea & Norman 2008; here and in the rest of the paper, J21 denotes the specific intensity just below 13.6eV, in the usual units of 10−21erg cm−2 sr−1…”
IONIZING PHOTON ESCAPE FRACTIONS FROM HIGH-REDSHIFT DWARF GALAXIES (2008, methodology): “The combination of lower temperatures and greater turbulent motions leads to turbulent Mach numbers above unity and close to the circular velocity of the halo, i.e. fturb = 1 (Wise & Abel 2007a; Greif et al. 2008).”