Photoevaporation of cosmological minihaloes during reionization

By P. Shapiro, Ilian Iliev, A. Raga. 2003

235 citations recorded by the source corpus.

Energy released by a small fraction of the baryons in the Universe, which condensed out while the intergalactic medium (IGM) was cold, dark and neutral, reheated and reionized it by redshift 6, exposing other baryons already condensed into dwarf-galaxy minihaloes to the glare of ionizing radiation. We present the first gas dynamical simulations of the photoevaporation of cosmological minihaloes overtaken by the ionization fronts which swept through the IGM during the reionization epoch in the currently favoured A cold dark matter (ACDM) universe, including the effects of radiative transfer. These simulations demonstrate the phenomenon of I-front trapping inside minihaloes, in which the weak, R-type fronts which travelled supersonically across the IGM decelerated when they encountered the dense, neutral gas inside minihaloes, and were thereby transformed into D-type I-fronts, preceded by shock waves. For a minihalo with virial temperature below 10 4 K, the I-front gradually burned its way through the minihalo which trapped it, removing all of its baryonic gas by causing a supersonic, evaporative wind to blow backwards into the IGM, away from the exposed layers of minihalo gas just behind the advancing I-front. We describe this process in detail, along with some of its observable consequences, for the illustrative case of a minihalo of total mass 10 7 M ○. , exposed to a distant source of ionizing radiation with either a stellar or quasar-like spectrum, after it was overtaken at redshift z = 9 by the weak, R-type I-front which ionized the IGM surrounding the source. For a source at z = 9 which emits 10 56 ionizing photons per second at 1 Mpc (or, equivalently, 10 52 ionizing photons per second at 10 kpc), the photoevaporation of this minihalo takes about 100-150 Myr, depending on the source spectrum, ending at about z = 7.5. Such hitherto neglected feedback effects were widespread during the reionization epoch. N-body simulations and analytical estimates of halo formation in the ACDM model suggest that sub-kpc minihaloes such as these, with virial temperatures below 10 4 K, were so common as to cover the sky around larger-mass source haloes and possibly dominate the absorption of ionizing photons during reionization. This means that previous estimates of the number of ionizing photons per hydrogen atom required to complete reionization which neglected this effect may be too low. Regardless of their effect on the progress of reionization, however, the minihaloes were so abundant that random lines of sight through the high-z Universe should encounter many of them, which suggests that it may be possible to observe the processes described here in the absorption spectra of distant sources.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

The birth of a galaxy – III. Propelling reionization with the faintest galaxies (2014, background): “3 that the halo–galaxy occupation fraction fhost decreases from an initial value f0 to a final value f1 after a sound-crossing time (cf. Shapiro et al. 2004; Sobacchi & Mesinger 2013) tsc ≈ 200 Myr ( M 108 M )1/3 ( 1 + z 10 )−1 ( mh 2 0.15 )−1/3 .”
Conditions for Reionizing the Universe with a Low Galaxy Ionizing Photon Escape Fraction (2019, background): “For the lowest-mass halos, ionization fronts in reionized regions will suppress star formation in minihalos with log(Mh/Me)8 (e.g., Shapiro et al. 2004).”
Efficient Simulations of Early Structure Formation and Reionization (2007, background): “However, a slight parallel for ionized islands in a mostly neutral IGM, could be found in Lyman limit systems (LLS) inside larger HII regions (e.g. Barkana & Loeb 2002; Shapiro et al. 2004; Miralda-Escudé et al. 2000), though it is not clear how prevalent such neutral clumps are at high redshifts.”
Cosmic Dawn (CoDa): the first radiation-hydrodynamics simulation of reionization and galaxy formation in the Local Universe (2015, background): “…is responsible for suppressing the star formation of low-mass galaxies, by removing gas from the smallest galaxies — minihalos — by photoevaporation (Shapiro et al. 2004; Iliev et al. 2005) and through the suppression of gas infall onto low-mass galaxies above the minihalo mass range, by…”
The morphology of H ii regions during reionization (2006, methodology): “By construction in the simulations of Shapiro et al. (2004), σ mh = π r2t at t = 0.”
Escape of Ionizing Radiation from High-Redshift Galaxies (2007, background): “…2000; Schaye et al. 2000; McDonald et al. 2001; Fechner & Reimers 2007), reducing gas accretion onto small dwarf galaxies (Efstathiou 1992; Thoul & Weinberg 1996; Dijkstra et al. 2004), and evaporating the existing gas in small halos (Barkana & Loeb 1999; Shaviv & Dekel 2003; Shapiro et al. 2004).”
Taxing the rich: Recombinations and bubble growth during reionization (2005, background): “We considered an extremely simple model to illustrate their possible effects; a more detailed look must consider the photoevaporation of these objects as they are ionized (Barkana & Loeb 1999; Shapiro et al. 2004), which makes the problem time-dependent.”
The First Stars (2003, background): “…feedback could be due to sources in the halo itself (e.g., Bromm et al. 2003, Oh & Haiman 2003, Whalen et al. 2003) or to an external ionizing background (e.g., Barkana & Loeb 1999, Susa & Umemura 2000, Kitayama et al. 2001, Dijkstra et al. 2004, Shapiro et al. 2004, Tassis et al. 2003).”
The Formation of the First Stars. II. Radiative Feedback Processes and Implications for the Initial Mass Function (2007, methodology): “The temperature of the ionized gas is 2:5 ; 104 K, based on themodels of Giroux & Shapiro (1996) and Shapiro et al. (2004) with stellar spectra.”
Self-regulated reionization (2006, background): “The minihalos are self-shielded, which results in their lower contribution to the total number of recombinations than one would infer from a simple gas clumping argument (Shapiro et al. 2004; Iliev et al. 2005b).”
Simulating cosmic reionization at large scales – II. The 21-cm emission features and statistical signals (2006, background): “…which results in their lower contribution to the total number of recombinations than one would infer from simple gas clumping argument (Shapiro et al. 2004; Iliev et al. 2005), while the larger halos are ionizing sources and their recombinations are implicitly included in the photon…”
Early Cosmological H II/He III Regions and Their Impact on Second-Generation Star Formation (2006, background): “However, since the maximum density of such small gas clumps is still 1 cm 3, they are quickly photoevaporated within the central star’s lifetime (Shapiro et al. 2004; Ahn & Shapiro 2006; Susa&Umemura 2006).”
Simulating Cosmic Reionization at Large Scales I: the Geometry of Reionization (2005, methodology): “This approximation breaks down in dense gas inside halos, where the I-fronts slow down and transform to a D-type (from “dense”, i.e. typically occurring in dense gas), generally preceded by a shock (Shapiro et al. 2004; Iliev et al. 2005b).”
The Baryon Content of Extremely Low Mass Dwarf Galaxies (2006, background): “…physical models have been proposed to explain high mass-to-light ratios in low mass galaxies, including photoevaporation of gas during reionization (Shapiro et al. 2004; Mayer & Moore 2004), suppression of gas accretion during reionization (Gnedin 2000; Bullock et al. 2000; Benson et al. 2003),…”