Recently the numerical simulations of the process of reionization of the
universe at z>6 have made a qualitative leap forward, reaching sufficient sizes
and dynamic range to determine the characteristic scales of this process. This
allowed making the first realistic predictions for a variety of observational
signatures. We discuss recent results from large-scale radiative transfer and
structure formation simulations on the observability of high-redshift Ly-alpha
sources. We also briefly discuss the dependence of the characteristic scales
and topology of the ionized and neutral patches on the reionization parameters.Comment: 4 pages, 5 figures (4 in color), to appear in Astronomy and Space
  Science special issue "Space Astronomy: The UV window to the Universe",
  proceedings of 1st NUVA Conference ``Space Astronomy: The UV window to the
  Universe'' in El Escorial (Spain

A. Bunker

D.N. Spergel

E.R. Stanway

G. Mellema

G.P. Holder

Garrelt Mellema

H. Trac

I.T. Iliev

Ilian T. Iliev

J.E. Rhoads

M.G. Santos

Marcelo A. Alvarez

O. Doré

O. Zahn

P. Madau

P. Tozzi

Patrick McDonald

Paul R. Shapiro

R.H. Becker

S.R. Furlanetto

Ue-Li Pen

W. Hu

X. Fan

English

arXiv

Crossref

Reionization: characteristic scales, topology and observability

Recently the numerical simulations of the process of reionization of the universe at z>6 have made a qualitative leap forward, reaching sufficient sizes and dynamic range to determine the characteristic scales of this process. This allowed making the first realistic predictions for a variety of observational signatures. We discuss recent results from large-scale radiative transfer and structure formation simulations on the observability of high-redshift Ly-a sources. We also briefly discuss the dependence of the characteristic scales and topology of the ionized and neutral patches on the reionization parameters

Ilian Iliev (4462258)

Ue-Li Pen (14358006)

Patrick McDonald (16059488)

Paul R Shapiro (16059491)

Garrelt Mellema (16059494)

Marcelo A Alvarez (16059497)

Sussex Research Online

Recently the numerical simulations of the process of reionization of the universe at z>6 have made a qualitative leap forward, reaching sufficient sizes and dynamic range to determine the characteristic scales of this process. This allowed making the first realistic predictions for a variety of observational signatures. We discuss recent results from large-scale radiative transfer and structure formation simulations on the observability of high-redshift Ly-α sources. We also briefly discuss the dependence of the characteristic scales and topology of the ionized and neutral patches on the reionization parameters

Iliev, I T

Pen, U L

McDonald, P

Shapiro, P R

Mellema, G

Alvarez, M A

ZORA

University of ZurichZurich Open Repository and ArchiveWinterthurerstr. 190CH-8057 Zurichhttp://www.zora.uzh.chYear: 2009Reionization: characteristic scales, topology and observabilityIliev, I T; Pen, U L; McDonald, P; Shapiro, P R; Mellema, G; Alvarez, M AIliev, I T; Pen, U L; McDonald, P; Shapiro, P R; Mellema, G; Alvarez, M A (2009). Reionization: characteristicscales, topology and observability. Astrophysics and Space Science, 320(1-3):39-43.Postprint available at:http://www.zora.uzh.chPosted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.chOriginally published at:Astrophysics and Space Science 2009, 320(1-3):39-43.Iliev, I T; Pen, U L; McDonald, P; Shapiro, P R; Mellema, G; Alvarez, M A (2009). Reionization: characteristicscales, topology and observability. Astrophysics and Space Science, 320(1-3):39-43.Postprint available at:http://www.zora.uzh.chPosted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.chOriginally published at:Astrophysics and Space Science 2009, 320(1-3):39-43.arXiv:0710.2451v1  [astro-ph]  12 Oct 2007Astrophysics and Space ScienceDOI 10.1007/sXXXXX-XXX-XXXX-XReionization: Characteristic Scales, Topology andObservabilityIlian T. Iliev • Paul R. Shapiro • Garrelt Mellema• Ue-Li Pen • Patrick McDonald • Marcelo A.Alvarezc© Springer-Verlag ••••Abstract Recently the numerical simulations of theprocess of reionization of the universe at z > 6 havemade a qualitative leap forward, reaching sufficientsizes and dynamic range to determine the character-istic scales of this process. This allowed making thefirst realistic predictions for a variety of observationalsignatures. We discuss recent results from large-scaleradiative transfer and structure formation simulationson the observability of high-redshift Ly-α sources. Wealso briefly discuss the dependence of the characteristicscales and topology of the ionized and neutral patcheson the reionization parameters.Keywords high-redshift — galaxies: formation — in-tergalactic medium — cosmology: theory — radiativetransfer — methods: numericalIlian T. IlievCanadian Institute for Theoretical Astrophysics, Uni-versity of Toronto, 60 St. George Street, Toronto, ONM5S 3H8, CanadaUniversität Zürich, Institut für Theoretische Physik,Winterthurerstrasse 190, CH-8057 Zürich, SwitzerlandPaul R. ShapiroDepartment of Astronomy, University of Texas, Austin,TX 78712-1083, U.S.A.Garrelt MellemaStockholm Observatory, AlbaNova University Center,Stockholm University, SE-106 91 Stockholm, SwedenUe-Li PenPatrick McDonaldCanadian Institute for Theoretical Astrophysics, Uni-versity of Toronto, 60 St. George Street, Toronto, ONM5S 3H8, CanadaMarcelo A. AlvarezKavli Institute for Particle Astrophysics and Cosmol-ogy, Stanford University, Stanford, CA 94305, USAFig. 1.— Large-scale geometry of reionization and thelarge local variations in reionization history as seen atredshifted 21-cm line: (top) lg(δTb) and (bottom) δTbsmoothed with 3’ compensated Gaussian beam.Fig. 2.— Ionization maps (blue neutral, red ionized) ofselected 100 h−1Mpc box simulations for high (bottompanels) and low source efficiencies (top) and with (rightpanels) and without (left panels) sub-grid clumping.2Fig. 3.— The reionization history of a high densitypeak. The images are centered on the most massive (atz = 6) halo in our computational volume and are ofsize 100h−1Mpc to the side. The snapshots are (leftto right): z = 12.9, z = 9.0, z = 8.0, and z = 6.6.The underlying cosmological density field (dark,green)is superimposed with the ionized fraction (light, orange)and the ionizing sources (dark, blue dots).Fig. 4.— Ly-α sources at redshift z = 6.0: Transmis-sion factor along sample lines-of-sight vs. λ/comovingdistance from the most massive galaxy in the compu-tational volume. There is significant transmission inthe proximity zone and transmission gaps in the meanIGM away from the source. Gas infall results in someabsorption red-ward of the line center.1 IntroductionThe observations of high-redshift QSO’s (Fan et al.2001; Becker et al. 2001) and large-scale CMB polar-ization (Spergel et al. 2007) indicate that the inter-galactic medium has been completely ionized by red-shift z ∼ 6 through an extended process. The mostprobable cause was the ionizing radiation of the FirstStars and QSO’s. Currently these are the two maindirect observational constraints on this epoch. Thisscarcity of observational data is set to change dra-matically in the next few years, however. A num-ber of large observational projects are currently un-der way, e.g. observations at the redshifted 21-cm lineof hydrogen (e.g. Madau et al. 1997; Tozzi et al. 2000;Iliev et al. 2002; Mellema et al. 2006; Furlanetto et al.2006), detection of small-scale CMB anisotropies dueto the kinetic Sunyaev-Zel’dovich (kSZ) effect (e.g. Hu2000; Santos et al. 2003; Iliev et al. 2007c), and surveysof high-redshift Ly-α emitters and studies of the IGMabsorption (e.g. Rhoads et al. 2003; Stanway and et al.2004; Bunker et al. 2006). The planning and successof these experiments relies critically upon understand-ing the large-scale geometry of reionization, i.e. thesize- and spatial distribution of the ionized and neu-tral patches. This is best derived by large-scale sim-ulations, although a number of semi-analytical mod-els exist as well (e.g. Furlanetto et al. 2004). Re-cently we presented the first large-scale, high-resolutionradiative transfer simulations of cosmic reionization(Iliev et al. 2006, 2007b) and applied those to derive arange of reionization observables (Mellema et al. 2006;Iliev et al. 2007c; Holder et al. 2007; Doré et al. 2007;Iliev et al. 2007a,d). Here we summarize recent resultson the characteristic scales and topology of reionizationand implications of our simulations for the observabilityof high-redshift Ly-α sources.2 Characteristic scales of ReionizationThe characteristic scales of the ionization and densityfluctuations are directly imprinted in the fluctuations ofall reionization observables (Fig. 1). It is thus critical tounderstand what these scales are and their dependenceson the (still not yet well-known) reionization parame-ters. We investigated the dependence of the character-istic sizes of ionized and neutral patches on some basicproperties of the sources of reionization and the inter-galactic medium, such as the halo mass-to-light ratio,susceptibility of haloes to positive and negative feed-back, and the gas clumping at small scales. We usedtwo independent methods for identifying the size distri-bution of patches, the friends-of-friends (FOF) methodReionization: Characteristic Scales, Topology and Observability 3Fig. 5.— Ly-α sources at redshift z = 6.0: Luminosityfunction without (black) and with absorption included(red). For reference, the green, dotted line shows theresult suppressing each source by 50%, which would bethe case if e.g. all of the blue wing of the emission line,but none of the red wing is absorbed.(Iliev et al. 2006), where all topologically-connectedionized regions are considered as one region, and thespherical average method (Zahn et al. 2007), where anaveraging over a spherical region and an ionizationthreshold are used to define the size. In the FOFmethod, throughout most of the evolution there is onevery large connected region in which most of the vol-ume is contained. For the spherical average method,the bubble distribution typically peaks on Mpc scales.Suppression of ionizing sources within ionized regionsand gas clumping both reduce the size and increase thenumber of H II regions, although the effect is modest,reducing the typical radius of H II regions by factors ofat most a few (Fig. 2). We also found that density andionized fraction are correlated on large scales, regardlessof the degree of clumping and suppression. The genus ofthe ionization field proved to be much more sensitive tosuppression and clumping than the size distributions orthe power spectra and could thus be used for more de-tailed characterization of the reionization parameters.We will present these results in detail in an upcomingpaper (Alvarez et al., in prep.).3 High-redshift Ly-α sourcesObservations of the high-redshift Ly-α sources haveprovided us with a wealth of information about thestate of the IGM and the nature of the galaxies atthe end of reionization and hold even more promise forthe future. In addition to probing the IGM and thesource luminosity function (and thus, indirectly, thehalo mass function and ionization source properties),they may also be used to constrain the reionizationtopology (Rhoads 2007). The first rare objects formin the highest peaks of the density field. The statisticsof Gaussian fields predicts that such peaks are stronglyclustered at high redshift. Hence each high-redshift,massive galaxy was surrounded by numerous smallerionizing sources. The self-consistent simulations of suchregions require following a large volume while also re-solving the low-mass halos driving reionization.In Figure 3 we illustrate several stages of the reion-ization history of a high density peak. The most mas-sive source in our volume (at z = 6) is shifted to thecentre using the periodicity of the computational box.At redshift z = 12.9 the source is invisible due to thedamping wing from the neutral gas outside the smallH II region. By redshift z = 9 many more haloeshave formed, most of them in large clustered groups.The H II region surrounding the central peak is amongthe largest, but the central source emission remainsstrongly affected by damping. Only by redshift z = 8the ionized region is large enough to render the sourcepotentially visible. The reionization geometry becomesquite complex, most ionized bubbles are interconnected,but large neutral patches remain between them, whichis also showing in the topological characteristics of thefiled like the genus discussed above. Finally, by thenominal overlap z = 6.6 all ionized regions have mergedinto one topologically-connected region, although sub-stantial neutral patches remain interspersed throughoutour volume, which is still largely optically-thick to bothLy-α and ionizing radiation. Only by z ∼ 6 this volumebecomes on average optically-thin to ionizing radiation.In Figure 4 we show some sample absorption spec-tra for the same luminous source. The spectra exhibitextended high-transmission (10-60% transmission) re-gions in the highly-ionized proximity zone of the lu-minous source, within 5 Mpch−1 (∼ 20 Å). The cen-ter of the peak itself is optically-thick due to its highdensity. The infall around the central peak blue-shiftsphotons, resulting in some transmission behind theredshift-space position of the source. Away from theproximity region the absorption is largely saturated,but there are a number of transmission gaps with upto a few per cent transmission. In Figure 5 we showthe Ly-α source luminosity function at the same red-shift. For the weaker sources roughly half of the intrin-sic luminosity is transmitted (the red wing of the line),while the most luminous sources suffer from additionalabsorption due to the gas infall that surrounds them.Future work will quantify the statistics of these featuresand its evolution.4ReferencesBecker, R.H., et, al.: Evidence for Reionization atz˜6: Detection of a Gunn-Peterson Trough ina z=6.28 Quasar. AJ 122, 2850–2857 (2001).doi:10.1086/324231Bunker, A., Stanway, E., Ellis, R., McMahon, R., Eyles, L.,Lacy, M.: Star forming galaxies at z∼6 andreionization. New Astronomy Review 50, 94–100(2006). doi:10.1016/j.newar.2005.11.006Doré, O., Holder, G., Alvarez, M., Iliev, I.T., Mellema, G.,Pen, U.L., Shapiro, P.R.: Signature of patchyreionization in the polarization anisotropy of theCMB. Phys. Rev. D 76(4), 043002–+ (2007).doi:10.1103/PhysRevD.76.043002Fan, X., et, al.: A Survey of z>5.8 Quasars in the SloanDigital Sky Survey. I. Discovery of Three NewQuasars and the Spatial Density of LuminousQuasars at z˜6. AJ 122, 2833–2849 (2001).doi:10.1086/324111Furlanetto, S.R., Oh, S.P., Briggs, F.H.: Cosmology atlow frequencies: The 21 cm transition and thehigh-redshift Universe. Phys. Reports 433, 181–301(2006). doi:10.1016/j.physrep.2006.08.002Furlanetto, S.R., Zaldarriaga, M., Hernquist, L.: TheGrowth of H II Regions During Reionization. ApJ613, 1–15 (2004)Holder, G.P., Iliev, I.T., Mellema, G.: Reconstructing theThomson Optical Depth due to Patchy Reionizationwith 21 cm Fluctuation Maps. ApJL 663, L1–L4(2007). doi:10.1086/519835Hu, W.: Reionization Revisited: Secondary Cosmic Mi-crowave Background Anisotropies and Polarization.ApJ 529, 12–25 (2000). doi:10.1086/308279Iliev I.T., Mellema G., Pen U.L., Bond J.R., Shapiro P.R.:Current models of the observable consequences ofcosmic reionization and their detectability. MNRASsubmitted, (astro-ph/0702099)Iliev, I.T., Mellema, G., Pen, U.L., Merz, H., Shapiro, P.R.,Alvarez, M.A.: Simulating cosmic reionizationat large scales - I. The geometry of reionization.MNRAS 369, 1625–1638 (2006). doi:10.1111/j.1365-2966.2006.10502.xIliev, I.T., Mellema, G., Shapiro, P.R., Pen, U.L.:Self-regulated reionization. MNRAS 376, 534–548(2007b). doi:10.1111/j.1365-2966.2007.11482.xIliev, I.T., Pen, U.L., Bond, J.R., Mellema, G.,Shapiro, P.R.: The Kinetic Sunyaev-Zel’dovichEffect from Radiative Transfer Simulations ofPatchy Reionization. ApJ 660, 933–944 (2007c).doi:10.1086/513687Iliev, I.T., Shapiro, P.R., Ferrara, A., Martel, H.: On theDirect Detectability of the Cosmic Dark Ages: 21Centimeter Emission from Minihalos. ApJL 572,L123–L126 (2002)Iliev I.T., Shapiro P.R., Mellema G., Pen U.L.,McDonald P., Bond J.R.: Simulating Reionization:Character and Observability. ArXiv e-prints 708(2007d)Madau, P., Meiksin, A., Rees, M.J.: 21 CentimeterTomography of the Intergalactic Medium at HighRedshift. ApJ 475, 429–+ (1997)Mellema, G., Iliev, I.T., Pen, U.L., Shapiro, P.R.:Simulating cosmic reionization at large scales - II.The 21-cm emission features and statistical signals.MNRAS 372, 679–692 (2006). doi:10.1111/j.1365-2966.2006.10919.xRhoads J.E.: Testing the Topology of Reionization. ArXive-prints 708 (2007)Rhoads, J.E., Dey, A., Malhotra, S., Stern, D., Spinrad, H.,Jannuzi, B.T., Dawson, S., Brown, M.J.I.,Landes, E.: Spectroscopic Confirmation of ThreeRedshift z˜5.7 Lyα Emitters from the Large-AreaLyman Alpha Survey. AJ 125, 1006–1013 (2003).doi:10.1086/346272Santos, M.G., Cooray, A., Haiman, Z., Knox, L., Ma, C.P.:Small-Scale Cosmic Microwave BackgroundTemperature and Polarization Anisotropies Dueto Patchy Reionization. ApJ 598, 756–766 (2003).doi:10.1086/378772Spergel, D.N., et, al.: Three-Year Wilkinson MicrowaveAnisotropy Probe (WMAP) Observations:Implications for Cosmology. ApJS 170, 377–408(2007). doi:10.1086/513700Stanway, E.R., et al., : Three Lyα Emitters at z ˜ 6: EarlyGMOS/Gemini Data from the GLARE Project.ApJL 604, L13–L16 (2004). doi:10.1086/383523Tozzi, P., Madau, P., Meiksin, A., Rees, M.J.: RadioSignatures of H I at High Redshift: Mapping theEnd of the “Dark Ages”. ApJ 528, 597–606 (2000)Zahn, O., Lidz, A., McQuinn, M., Dutta, S., Hernquist, L.,Zaldarriaga, M., Furlanetto, S.R.: Simulations andAnalytic Calculations of Bubble Growth duringHydrogen Reionization. ApJ 654, 12–26 (2007).doi:10.1086/509597This manuscript was prepared with the AAS LATEX macrosv5.2.

Reionization: Characteristic Scales, Topology and Observability

Reionization: Characteristic Scales, Topology and Observability

Abstract

Similar works

Full text

Available Versions

Crossref

Sussex Research Online

ZORA