1. Observational Constraints of of Reionization History in the JWST Era Observational Constraints of of Reionization History in the JWST Era Xiaohui Fan University of Arizona Background: 46,420 Quasars from the SDSS Data Release Three Astrophysics in the Next Decade Sep 26, 2007

2. From Avi Loeb reionization Two Key Constraints: 1.WMAP 3-yr: z reion =10+/-3 2. IGM transmission: z reion > 6

3. Outline Current Observational Constraints Probing reionization history in the next decade –Finding high-z sources –Observational tests for the neutral era Two critical tasks related to JWST –Wide-field IR surveys for z>8 quasars –Comprehensive Ly  galaxy surveys at z~10 Will not talk about: –21cm probe –Future CMB polarization measurements –IR background and first stars

4. Three stages Pre-overlap Overlap Post-overlap From Haiman & Loeb

5. Open Questions: When did it happen: f HI vs. z –z~6: late –z~15: early –Extended or phase transition? How did reionization proceed: –Homogeneous or large scatter?  (f HI ) vs. z –Topology of overlap; f HI vs.  What did it:  (gal, qso) vs. z –AGN? –Star formation? –Decay particles? Observational goals –Map the evolution and spatial distribution of ionization state –Find highest redshift galaxies and quasars: source of reionization

6. WMAP: early reionization? WMAP third year: –  = 0.09+/- 0.03 –Larger signal comparing to late reionization model (but marginally consistent!) However, no direct conflict to Gunn-Peterson result, which is sensitive only to ~1% neutral IGM Overlapping could still be at z~6 IGM could have complex reionization history  direct observation of high-z sources Page et al., Spergel et al. 2006 z reion = 6

7. Gunn-Peterson Test Classic G-P (1965) effect: –Saturates at low neutral fraction G-P damping wing (Miralda-Escude 1998) –Sensitive to neutral IGM –Attenuates off-resonance transmissions Damping wing

9. Evolution of Lyman Absorptions at z=5-6  z = 0.15

10. Accelerated Evolution at z>5.7 Optical depth evolution accelerated –z<5.7:  ~ (1+z) 4.5 –z>5.7:  ~ (1+z) >11 –End of reionization? Evolution of neutral fraction –f HI > 10 -3 - 10 -2 at z=6 –Order of magnitude increase from z~5 –G-P absorption saturates; needs more sensitive tests (1+z) 4.5 (1+z) 11 XF et al. 2006

11. HII regions around high-z quasars Size of HII region R p ~ (L Q t Q / f HI ) 1/3 Best estimate: f HI ~ a few percent at z~6 Can be applied to higher z and f HI with lower S/N data XF et al. 2006 Shapiro, Haiman, Mesinger, Wyithe, Loeb, Bolton, Haehnelt, Maselli et al. HII region size (Mpc) redshift Damping wing at the edge of quasar HII region Mesinger and Haiman

12. Beyond Gunn-Peterson Optical Depth: HII Region Sizes and Dark Gap Distributions Size of HII region R s ~ (L Q t Q / f HI ) 1/3 Best estimate: f HI ~ a few percent at z~6 Can be applied to higher z and f HI with lower S/N data Shapiro, Haiman, Mesinger, Wyithe, Loeb, Bolton, Haehnelt, Maselli et al. Dark gap statistics – Sensitive to the topology of reionization z~6 observations: – Dramatic increase in gap length: Consistent with overlap at z~6-8 – Existence of transmission at z>6 places an upper limit of average neutral fraction <30% (Gallerani et al. 2007) Gallerani et al. z em

13. Dark Gap Distributions Dark gap statistics (Songaila & Cowie 2002) –Gaps: regions where all pixels have  >2.5 –Sensitive to the topology of reionization Gaps among z~6 quasars – dramatic increase in gap length: Consistent with overlap at z~6-8 Upper limit on neutral fraction –If IGM largely neutral, GP damping wing will wipe out all HII region transmissions –Existence of transmission at z>6 places an upper limit of average neutral fraction <30% (Gallerani et al. 2007) XF et al. 2006 Gallerani et al.

14. Iye et al. 2006 Kashikawa et al. 2006 Ota et al. 2007 Ly  Galaxy LF at z>6 Neutral IGM has extended GP damping wing  attenuates Ly  emission line New Subaru results –Declining density at z~6-7 (2-3  result) –Reionization not completed by z~6.5 –f HI ~ 0.3 - 0.6 at z~7 –Overlapping at z=6-7? –cf. Malhotra & Rhoads, Hu et al.: lack of evolution in Ly  galaxy density

15. GRBs as Probes of Reionization Detected to z=6.30 Advantages: –Bright –Small surrounding HII regions: could use damping wing of Gunn- Peterson trough to probe high neutral fraction Constraining neutral fraction –How to distinguish internal absorption from IGM damping wing?? –Using 050904: f HI < 0.6 (2- sigma) by fitting both DLA and IGM profiles Damping wing? GRB050904 Kawai et al. 2005

16. What Ionized the Universe? AGNs or Galaxies SFR of galaxies Density of quasars Depends on: –Luminosity density: Detailed LF and IMF –Escape fraction of ionizing photons to the IGM: Quasar: f esc ~1 Galaxies?? –Clumpiness of the IGM Can quasars do it? Not likely –Too few quasars unless QLF remains to be steep to AGN luminosity –Extra constraints from X-ray background Reionization Budget

17. Reionization by stellar sources? Necessary for reionization 6<z<9 (Stiavelli et al 2003) Large uncertainties in reionization photon budget: –IGM clumpiness; IMF; escape efficiency –Large cosmic (sample) variance in deep field data –Galaxy luminosity function at high-z Sources of reionization have not been identified! –Most likely dwarf galaxies Bouwens & Illingworth; Bunker et al. ; Gnedin Yan and Windhorst

18. Probing Reionization History Fan, Carilli & Keating 2006

19. Quest to the Highest Redshift

20. Next Generation Quasar Surveys Optical surveys: limited to z<7 New generations of red-sensitive CCD devices –Improved QE at 1 micron (Y band) –SUBARU/Princeton (2010+): a few hundred deg, Y<25;? –Pan-Starrs (2008+): 3  : Y<22.5; 1000 deg 2 : Y<24; 30 deg 2 : Y<26 –LSST (2013+): 3  : Y< 25 –Discovery of large number of quasars at z<7.5 New generation of Near-IR surveys: –UKIDSS (2005 - 2012?): 4000 deg 2: J AB <21 –VISTA/VHS (2008+): 20000 deg 2: J AB <21 –VISTA/VIKING (2008+): 1500 deg 2: J AB <22 –VISTA/VIDEO (2008+): 15 deg 2: J AB <24.5 –Discovery of a handful of quasars at z=7-9

21. Probing Neutral Era with JWST Quasar Observations HII Region Sizes –Radiative transfer effect –Large scatter on individual HII region sizes –Need large sample of quasars but at low S/N Gallerani et al. Dark Gap Statistics –Sensitive to overlapping topology –Requires moderate spectral resolution and high S/N Bolton and Haehnelt

22. Probing the Neutral Era with JWST Quasar Spectroscopy Measuring G-P optical depth –R~100 mode for faint AGNs –Insensitive to neutral era Measuring HII region sizes –R~1000 mode –Sensitive to high f HI –Radiative transfer effects causing large scatter for individual object –Modest S/N but require large sample –J AB <24.5 (deep surveys) JWST/NIRspec 300k sec Probing reionization using dark gap distribution: –R~2700 mode –Sensitive to overlap topology –J AB <22.5 (wide surveys!)

23. Evolution of IGM Metals Early Enrichment of the IGM by First stars –Lack of evolution in metal line density up to z~6 OI Forest (Oh 2002) –OI and H have almost identical ionization potentials –In charge exchange equilibrium with H but much lower abundance –Fluctuating OI forest during neutral era to probe ionization topology and metal pollution in the IGM OI system at z=6.26 Becker et al. 2006 Ryan-Weber et al. Evolution of CIV systems

24. Will there be enough quasars? For z>9 (assuming quasar LF evolution has not steepened) –Bright (AB<22.5): 0.2/100 deg 2 –Faint (AB<24.5): 1-10/100 deg 2 difficult for current or planned ground-based IR surveys to find enough quasars for JWST reionization probes… Number expected Based on z~6 QLF

25. Spitzer Warm Mission Survey? Wide-field IRAC survey as path-finder to JWST (Gardner, XF, Wilson, Stiavelli) –500 deg 2 to SWIRE depth –Combined with deep optical/near-IR data for selection

26. 4yr ½yr eROSITA e-ROSITA All sky X-ray survey –PI. G. Hasinger –Launch 2011 –Expect: 60 quasars at z>7 20 at z>8 5 at z>9

27. Lyman  Emitter at z~10? Keck blind spectroscopic survey along critical lines of high-z clusters –Six promising Ly  emitter candidates at z=8.7 - 10.2 –Large abundance of low-L galaxies; providing sufficient reionization photons –Limit of ground-based search; extremely difficult to confirm spectroscopically Stark, Ellis et al.

28. Ground-based Ly  surveys DAZEL - The Dark Age Z(redshift) Lyman-  Explorer on VLT: – dedicated Ly  narrow band survey instrument for z=7 - 10 – ~ 1 object per 10 hour field New generation of OH suppression technique and AO: –Ground-based surveys could find Ly  emitters at z<12 McMahon et al. J H K Bland-Hawthorn

29. Reionization Topology with Ly  Emitters Ly  emitter could provide sensitive probe to reionization history, especially during overlapping –Evolution of LF (constrain f HI ) –Clustering –genus numbers Distribution of Ly  emitters over JWST FOV McQuinn et al. Angular correlation of Ly  emitters Neutral  Ionized

30. Ly  Emitter Surveys in JWST Era Interpretation of Ly  emitters alone is highly model dependent: –Evolution of continuum LF –Uncertainties in Ly  radiative transfer –Intrinsic clustering of galaxies etc. Requires surveys of continuum and SF selected samples intrinsic observed · Ly  selected  continuum selected Rhoads 2007

31. Synergetic survey of galaxies in reionization era NIRSpec FGS/TFI

32. Synergetic Survey of Galaxies in Reionization Era JWST will detect sources that reionization the Universe at z>10 –Ability to find high-z sources limited by whether the Universe managed to make them Ground-based and JWST/TFI will detect Ly  and HeII emitters to probe reionization history and topology ALMA will provide dust/star- formation/dynamics Windhorst et al.

33. Wish List to Theorists Reionization Simulation –Volume: hundreds of Mpc –Resolution: dwarf galaxy halos and Lyman Limit Systems –Radiative transfer –Star formation prescriptions –Contribution from Pop III Ly  emission physics Understanding escape fraction of ionization photons Gnedin and Fan 2006

34. Escape Fraction: A Key Uncertainty Escape fraction (as a function of z, L, age) affects: –Total reionization budget –HII region sizes – Ly  emitter probe Current measurements extremely uncertain –Shapley et al. at z~3: 2/14 detections –Siana et al. at z~1: f esc <0.02; evolution? –Large HST surveys underway But how to measure it at z>6??? Siana et al. 2007

35. Summary What do we know now about reionization? –z rei = 6 - 13 –Overlapping probably late with extended reionization process –AGN not likely sources of reionization; situation for galaxies uncertain What do we expect to know before JWST –Reionization history to z~8 from quasars/GRBs Needs more powerful quasar surveys (Spitzer warm and eROSITA) –Small number of Ly  emitters at z=7 - 10 –Lyman break-selected population at z~8-10 from WFC3: better constraints on reionization budget –Progress in reionization simulations Roles of JWST –Absorption line probes using high-z quasars –Identify the reionization population –Mapping out Ly  emitters at the peak of reionization, synergy with ALMA and GSMT/ELT

36. Probing Reionization History JWST, GSMT 21cm, GRB, ALMA Fan, Carilli, Keating 2006