Simulating Cosmic Reionization at Large Scales I: the Geometry of Reionization

By Ilian Iliev, G. Mellema, Ue-Li Pen, Hugh Merz, P. Shapiro, M. A. A. Cita, Astron, Dwingeloo, L. Observatory, U. T. A. Austin. 2005

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We present the first large-scale radiative transfer simulat ions of cosmic reionization, in a simulation volume of (100 h 1 Mpc) 3 . This is more than a 2 orders of magnitude improvement over previous simulations. We achieve this by combining the results from extremely large, cosmological, N-body simulations with a new, fast and effici ent code for 3D radiative transfer, C 2 -Ray, which we have recently developed. These simulations allow us to do the first numerical studies of the large-scale structure of reionization w hich at the same time, and crucially, properly take account of the dwarf galaxy ionizing sources which are primarily responsible for reionization. In our realization, reionization starts around z � 21, and final overlap occurs by z � 11. The resulting electron-scattering optical depth is in goo d agreement with the firstyear WMAP polarization data. We show that reionization clearly proceeded in an inside-out fashion, with the high-density regions being ionized earli er, on average, than the voids. Ionization histories of smaller-size (5 to 10 comoving Mpc) subregions exabit a large scatter about the mean and do not describe the global reionization history well. This is true even when these subregions are at the mean density of the universe, which shows that small-box simulations of reionization have little predictive power for the evolut ion of the mean ionized fraction. The minimum reliable volume size for such predictions is � 30 Mpc. We derive the power-spectra of the neutral, ionized and total gas density fields and show t hat there is a significant boost of the density fluctuations in both the neutral and the ionized c omponents relative to the total at arcminute and larger scales. We find two populations of H II re gions according to their size, numerous, mid-sized (� 10 Mpc) regions and a few, rare, very large regions tens of Mpc in size. Thus, local overlap on fairly large scales of tens of Mp c is reached by z � 13, when our volume is only about 50% ionized, and well before the global overlap. We derive the statistical distributions of the ionized fraction and ionized gas densi ty at various scales and for the first time show that both distributions are clearly non-Gaussian. All these quantities are critical for predicting and interpreting the observational signals from reionization from a variety of observations like 21-cm emission, Ly-α emitter statistics, Gunn-Peterson optical depth and small-scale CMB secondary anisotropies due to patchy reionization.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

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Citations in the corpus

Lyα Emitting Galaxies as a Probe of Reionisation (2014, background): “…and large-scale simulations is one in which the early stages of reionisation are characterised by the presence of HII bubbles centred on overdense regions of the Universe, completely separated from each other by a neutral IGM (Furlanetto et al. 2004; Iliev et al. 2006; McQuinn et al. 2007).”
EVIDENCE FOR PopIII-LIKE STELLAR POPULATIONS IN THE MOST LUMINOUS Lyα EMITTERS AT THE EPOCH OF REIONIZATION: SPECTROSCOPIC CONFIRMATION (2015, background): “…are particularly important to test and refine models of galaxy formation and evolution (e.g. Vogelsberger et al. 2014; Schaye et al. 2015) and to study the epoch of re-ionisation (e.g. Shapiro et al. 1994; Sokasian et al. 2004; Furlanetto et al. 2004; McQuinn et al. 2006; Iliev et al. 2006).”
ramses-rt: radiation hydrodynamics in the cosmological context (2013, methodology): “Comparative evaluations of both methods have been performed in several papers (Iliev et al. 2006b, 2009; Altay, Croft & Pelupessy 2008; Aubert & Teyssier 2008; Pawlik & Schaye 2008, 2011; Maselli, Ciardi & Kanekar 2009; at U niversitaet Z uerich on February 11, 2014…”
Cosmological Parameter Estimation Using 21 cm Radiation from the Epoch of Reionization (2005, background): “Recent simulations have made significant strides toward attaining these goals (Iliev et al. 2006;Kohler&Gnedin 2005).”
The GMRT Epoch of Reionization experiment: a new upper limit on the neutral hydrogen power spectrum at z≈ 8.6 (2010, background): “…patchy topology is well motivated by theory and simulations ⋆ Email:paciga@astro.utoronto.ca † Email:pen@cita.utoronto.ca (e.g. Furlanetto et al. 2004; Iliev et al. 2006; McQuinn et al. 2007; Zahn et al. 2007; see Trac & Gnedin 2009 for a review) though the exact properties are poorly constrained.”
Efficient Simulations of Early Structure Formation and Reionization (2007, background): “We note, however, that the situation at high redshifts is less clear: studies disagree on the relative accuracy of the Press & Schechter (1974) and Jenkins et al. (2001) forms (Reed et al. 2003; Iliev et al. 2006b; Zahn et al. 2007).”
Radiative Transfer Simulations of Cosmic Reionization. I. Methodology and Initial Results (2006, methodology): “Large-volume but low-resolution simulations (e.g., Sokasian et al. 2003; Ciardi et al. 2003; Kohler et al. 2007; Iliev et al. 2006, 2007; Zahn et al. 2007;McQuinn et al. 2007) enable the study of the large-scale structure of dark matter, baryons, sources, and H ii regions, but theymust correct for…”
Resolving cosmic structure formation with the Millennium-II simulation (2009, methodology): “…with & 1010 particles within smaller volumes (Lbox ≈ 100h−1 Mpc) have been used primarily for studying cosmic reionization at redshifts & 6 (e.g., Iliev et al. 2006). details of the parameters which define this simulation and describes some of the post-processing we have carried out on its…”
COSMIC MICROWAVE BACKGROUND CONSTRAINTS ON THE DURATION AND TIMING OF REIONIZATION FROM THE SOUTH POLE TELESCOPE (2011, background): “Recently, some groups have come close to achieving this dynamic range in a single simulation (Iliev et al. 2006; McQuinn et al. 2007b; Trac & Cen 2007a; Shin et al. 2008; Trac et al. 2008; Zahn et al. 2011; see Trac & Gnedin 2011 for a recent review).1 Given the large uncertainties in the…”
Self-regulated reionization (2006, methodology): “…conditions in the radiative transfer 2 The integrated electron-scattering optical depths for ourlarge-box simulations were estimated incorrectly in Iliev et al. (2006b) and Mellema et al. (2006b), the correct, slightly lower, values are listed in Table 1 c© 2006 RAS, MNRAS000, 1 simulations are…”
UV Luminosity Functions at z~4, 5, and 6 from the Hubble Ultra Deep Field and Other Deep Hubble Space Telescope ACS Fields: Evolution and Star Formation History (2007, background): “…medium are not quite right and that one should use a smaller value for the clumping factor (e.g., Bolton & Haehnelt 2007; Sokasian et al. 2003; Iliev et al. 2006; Sawicki & Thompson 2006b) or higher temperature for the IGM (e.g., Stiavelli et al. 2004) than has been assumed in many previous…”
Cosmic Dawn (CoDa): the first radiation-hydrodynamics simulation of reionization and galaxy formation in the Local Universe (2015, methodology): “For this simulation to characterize the evolving ”patchiness” of reionization in a statistically meaningful way requires a a comoving simulation volume as large as ∼ (100 Mpc)3 [e.g. (Iliev et al. 2006, 2014)].”
The First Billion Years project: the escape fraction of ionizing photons in the epoch of reionization (2015, background): “…semi-analytic modelling of reionisation (e.g. Choudhury et al. 2009; Pritchard et al. 2010; Santos et al. 2010; Mesinger et al. 2011; Raskutti et al. 2012; Mitra et al. 2013; Shull et al. 2012) and numerical simulations of reionisation (e.g. Iliev et al. 2006; Trac & Cen 2007; Ciardi et al. 2012).”
Cosmological radiative transfer codes comparison project – I. The static density field tests (2006, unknown): “The code is currently used for large-scale simulations of cosmic reionization and its observability (Iliev et al. 2006b; Mellema et al. 2006b) on grid sizes up to 4063 and up to more than 105 ionizing sources.”
Charting the parameter space of the global 21-cm signal (2016, background): “According to current understanding, reionization happens inside out, proceeding first in the dense regions containing most of the sources (Barkana & Loeb 2004; Furlanetto et al. 2004; Iliev et al. 2006).”
The Halo Mass Function: High-Redshift Evolution and Universality (2007, methodology): “…al. 2003, ST, orWarren) at low redshift (Reed et al. 2003, 2007; Springel et al. 2005; Heitmann et al. 2006a; Maio et al. 2006; Zahn et al. 2007) or consistent with the PS fit (Jang-Condell & Hernquist 2001; Yoshida et al. 2003a, 2003b, 2003c; Cen et al. 2004; Iliev et al. 2006; Trac & Cen 2006).”
Simulating cosmic reionization: how large a volume is large enough? (2013, methodology): “As we showed above, the mean reionization history is alreadywell converged for∼ 100 Mpc volumes (or even for ones of few tens of Mpc across, see Iliev et al. 2006).”
A case study of hurdle and generalized additive models in astronomy: the escape of ionizing radiation (2018, background): “…2013), semi-analytical (e.g. Choudhury, Haehnelt & Regan 2009; Pritchard, Loeb & Wyithe 2010; Santos et al. 2010; Mesinger, Furlanetto & Cen 2011; Shull et al. 2012a; Mitra, Ferrara & Choudhury 2013) as well as simulated (e.g. Iliev et al. 2006; Trac & Cen 2007; Ciardi et al. 2012) investigations.”
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).”