The morphology of H ii regions during reionization

By M. McQuinn, A. Lidz, Oliver Zahn, S. Dutta, L. Hernquist, M. Zaldarriaga. 2006

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It is possible that the properties of H II regions during reionization depend sensitively on many poorly constrained quantities [the nature of the ionizing sources, the clumpiness of the gas in the intergalactic medium (IGM), the degree to which photoionizing feedback suppresses the abundance of low-mass galaxies, etc.], making it extremely difficult to interpret upcoming observations of this epoch. We demonstrate that the actual situation is more encouraging, using a suite of radiative transfer simulations, post-processed on outputs from a 1024 3 , 94-Mpc N-body simulation. Analytic prescriptions are used to incorporate small-scale structures that affect reionization, yet remain unresolved in the N-body simulation. We show that the morphology of the H II regions for reionization by POPII-like stars is most dependent on the global ionization fraction x i . Changing other parameters by an order of magnitude for fixed x i often results in similar bubble sizes and shapes. The next most important dependence is on the properties of the ionizing sources. The rarer the sources, the larger and more spherical the H II regions become. The typical bubble size can vary by as much as a factor of 4 at fixed x i between different possible source prescriptions. The final relevant factor is the abundance of minihaloes or of Lyman-limit systems. These systems suppress the largest bubbles from growing, and the magnitude of this suppression depends on the thermal history of the gas as well as the rate at which these systems are photo-evaporated. We find that neither source suppression owing to photo-heating nor small-scale gas clumping significantly affects the large-scale structure of the H II regions, with the ionization fraction power spectrum at fixed x i differing by less than 20 per cent for k < 5 Mpc -1 between all the source suppression and clumping models we consider. Analytic models of reionization are successful at predicting many of the features seen in our simulations. We discuss how observations of the 21-cm line with the Mileura Widefield Array (MWA) and the Low Frequency Array (LOFAR) can constrain properties of reionization, and we study the effect patchy reionization has on the statistics of Lyα emitting galaxies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/2e3e02b0bb8e317855f470917c77f755ac87dd3d

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Citations in the corpus

New Limits on 21cm EoR From PAPER-32 Consistent with an X-Ray Heated IGM at z=7.7 (2013, background): “In the literature to date, sensitivity derivations have commonly assumed a top-hat beam response or a sinc response in the uv-plane (see, e.g., Morales 2005, McQuinn et al. 2006, and P12a).”
Reionization and Cosmology with 21-cm Fluctuations (2009, background): “However McQuinn et al. (2006) found that planned low frequency arrays like MWA and LOFAR will not be sensitive to the µ4 term, and so could only provide useful cosmological constraints in a situation where density fluctuations dominate the 21 cm PS.”
NEW OBSERVATIONS OF z ∼ 7 GALAXIES: EVIDENCE FOR A PATCHY REIONIZATION (2014, background): “The expected cumulative distribution function of restframe EWs for z∼ 7 LBGs, under the assumption that the observed LAE fraction at z ∼ 7 is different from z∼ 6 only because of the IGM.”
Reionization and the Cosmic Dawn with the Square Kilometre Array (2012, methodology): “…HI gas density field, which contribute to the 21cm signal, should trace those of the underlying CDM, and thus, of the fundamental cosmological parameters that define the power spectrum of the linear density field (Tozzi et al. 2000; Zaldarriaga et al. 2004; Bowman et al. 2007; McQuinn et al. 2006).”
Science with the Murchison Widefield Array (2012, methodology): “Theoretical studies suggest that the distribution of neutral gas during reionisation is very inhomogeneous (e.g. McQuinn et al. 2007).”
Fast large volume simulations of the 21-cm signal from the reionization and pre-reionization epochs (2009, background): “…simulation), plus a full radiative transfer code to propagate the ionizing radiation (Gnedin 2000; Razoumov et al. 2002; Sokasian et al. 2003; Ciardi et al. 2003; Kohler et al. 2005; Iliev et al. 2006; Zahn et al. 2007; McQuinn et al. 2007; Shin et al. 2007; Trac & Cen 2007; Baek et al. 2009).”
21cmfast: a fast, seminumerical simulation of the high‐redshift 21‐cm signal (2010, background): “Preliminary studies therefore concluded that redshift space distortions would only be noticeable before reionization and in its early stages (McQuinn et al. 2006, MF07).”
Inferences on the timeline of reionization at z ∼ 8 from the KMOS Lens-Amplified Spectroscopic Survey (2019, methodology): “As the size of ionised regions during reionization is expected to be nearly independent of redshift at fixed xhi (as there is little difference in the matter power spectrum from z ∼ 7 − 11, McQuinn et al. 2007), we use the same z ∼ 7 cubes as used by M18a rather than generating new z ∼ 8 cubes.”
The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6 (2010, background): “In the future 21 cm tomography has the potential to add strong constraints on cosmological parameters (e.g., McQuinn et al. 2006; Cooray et al. 2008; Mao et al. 2008; Furlanetto et al. 2009; Masui et al. 2010).”