Simulating cosmic reionization: how large a volume is large enough?

By Ilian Iliev, G. Mellema, K. Ahn, P. Shapiro, Y. Mao, Ue-Li Pen. 2013

137 citations recorded by the source corpus.

We present the largest-volume (425 Mpc h(-1) = 607 Mpc on a side) full radiative transfer simulation of cosmic reionization to date. We show that there is significant additional power in density fluctuations at very large scales. We systematically investigate the effects this additional power has on the progress, duration and features of reionization and on selected reionization observables. We find that comoving volume of similar to 100 Mpc h(-1) per side is sufficient for deriving a convergent mean reionization history, but that the reionization patchiness is significantly underestimated. We use jackknife splitting to quantify the convergence of reionization properties with simulation volume. We find that sub-volumes of similar to 100 Mpc h(-1) per side or larger yield convergent reionization histories, except for the earliest times, but smaller volumes of similar to 50 Mpc h(-1) or less are not well converged at any redshift. Reionization history milestones show significant scatter between the sub-volumes, as high as Delta z similar to 1 for similar to 50 Mpc h(-1) volumes. If we only consider mean-density sub-regions the scatter decreases, but remains at Delta z similar to 0.1-0.2 for the different size sub-volumes. Consequently, many potential reionization observables like 21-cm rms, 21-cm PDF skewness and kurtosis all showgood convergence for volumes of similar to 200 Mpc h(-1), but retain considerable scatter for smaller volumes. In contrast, the three-dimensional 21-cm power spectra at large scales (k < 0.25 h Mpc(-1)) do not fully converge for any sub-volume size. These additional large-scale fluctuations significantly enhance the 21-cm fluctuations, which should improve the prospects of detection considerably, given the lower foregrounds and greater interferometer sensitivity at higher frequencies.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/577c97254bf343306b7700f575421eec275effb8

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Citations in the corpus

The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, methodology): “An accurate model of reionization must include realistic large-scale IGM structure (Trac et al. 2008; Iliev et al. 2014; Sobacchi & Mesinger 2014).”
Galaxy Protoclusters as Drivers of Cosmic Star Formation History in the First 2 Gyr (2017, background): “1 are reminiscent of the ionizing bubbles seen in overdense regions in simulations of cosmic reionization (Ciardi et al. 2003; McQuinn et al. 2007; Iliev et al. 2014).”
Can the intergalactic medium cause a rapid drop in Lyα emission at z > 6? (2014, methodology): “Here we develop the most comprehensive model of IGM absorption to date, including the impact of both (i) the large-scale (hundreds of cMpc; e.g. Iliev et al. 2014) reionization morphology; and (ii) ∼kpc scale (e.g. Schaye 2001) self-shielded systems.”
GRACKLE: a chemistry and cooling library for astrophysics (2016, background): “This could be done as a post-processing step, usually for cosmic reionization calculations (e.g. Iliev et al. 2014; Mesinger et al. 2016), or coupled with the hydrodynamics, which is becoming more commonplace in galaxy and star formation simulations (e.g. Wise et al. 2014; Rosdahl et al. 2015;…”
The realm of the galaxy protoclusters (2016, background): “13 in Iliev et al., 2014).”
The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization (2015, background): “The topology of reionisation has to be studied using largevolume simulations to make sure the results are unbiased (Iliev et al. 2014).”
A case study of hurdle and generalized additive models in astronomy: the escape of ionizing radiation (2018, background): “…Epoch of Reionization (EoR) represents a milestone in the evolution of the Universe marking the transition from an initially neutral inter-galactic medium (IGM) into a hot, ionized plasma (e.g. Gnedin 2000; Ciardi, Stoehr & White 2003; Iliev et al. 2014; Dayal & Ferrara 2018; Eide et al. 2018).”
Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “…& Cen 2007; Dayal et al. 2008; Mitra et al. 2015; Mutch et al. 2016) or are based on large scale simulations (e.g. Gnedin 2014; Ricotti et al. 2002; Iliev et al. 2006, 2014; Ocvirk et al. 2016), and all of them use fesc directly or indirectly, the fraction of ionizing photons that escape the…”
Cosmic Dawn (CoDa): the first radiation-hydrodynamics simulation of reionization and galaxy formation in the Local Universe (2015, methodology): “…(although somehow controversial) in the literature for the choice of the escape fraction, we can consider two limiting cases: • the large scale, low spatial resolution regime, where the radiative transfer grid cells size is larger than the galaxies, e.g. dx= 0.44 h−1Mpc as in Iliev et al. (2014).”