Observational Constraints of Observational Constraints of the Epoch - - PowerPoint PPT Presentation

Observational Constraints of Observational Constraints of the Epoch of the Epoch of Reionization Reionization

Xiaohui Xiaohui Fan Fan University of Arizona University of Arizona

Collaborators: Becker, Carilli, Ferrara, Gallerani, Gnedin, Jiang, Richards, Roy Choudhury, Strauss, Xu, Walter, White, et al.

Background: 46,420 Quasars from the SDSS Data Release Three

From Avi Loeb

reionization

Two Key Constraints:

• 1. WMAP 3-yr: zreion=10+/-3
• 2. IGM transmission: zreion > 6

Three stages

Pre-

• verlap

Overlap Post-overlap

From Haiman & Loeb

Open Questions:

• When: Early or Late

– z~6: late – z~15: early

• How did reionization proceed:

– Phase transition or gradual? – Once or twice? – Homogeneous or large scatter?

• What did it:

– AGN? – Star formation? – Decay particles?

• Observational goals

– Map the evolution of ionization state: neutral fraction (fHI) vs. redshift – Find highest redshift galaxies and quasars: source of reionization

WMAP: early reionization?

• Thompson scattering of

CMB photons by free electrons during/after reionization

• -> polarization
• WMAP third year:

– τ = 0.09+/- 0.03 – Larger signal comparing to late reionization model (but marginally consistent!)

Page et al., Spergel et al. 2006 zreion = 6

WMAP: early reionization

• Inconsistent with a phase

transition at z=6 at 2 σ level

• Reionization could starts

at z=10-15

• However, no direct

conflict to Gunn-Peterson result, which is sensitive

• nly to ~1% neutral IGM
• Overlapping could still be

at z~6

• IGM could have complex

reionization history ⇒ direct observation of high-z sources

Gnedin 2004

Spergel et al. 2006

Quest to the Highest Redshift Quasars

• SDSS

Radio APM CCD

IR survey (UKIDSS, VISTA)

The Highest Redshift Quasars Today

• z>4: >1000 known
• z>6: 19
• SDSS i-dropout Survey:

– Completed in June 2006:

• 7700 deg2, zAB < 20
• 27 luminous quasars at

5.71<z<6.42

• CFHT High-z Quasar Survey

(CFHTQS, Willott et al. astro- ph/0706091)

– Goal: 400 deg2, zAB<22.5 – 4 quasars at z>6 – New highest-z quasar at z=6.43

• SDSS Faint Quasar Survey (SFQS):

– faint quasars in the deep SDSS stripe (Jiang, XF et al.), – 300 deg2, zAB < 22.5 – six z~6 quasar at 20 < zAB < 21 – Goal: quasar LF

• Other on-going z~6 quasar

surveys:

– AGES (Cool et al.): Spitzer selected, one quasar at z=5.8 – FIRST-Bootes (Becker et al.): radio selected, one quasar at z=6.1 – QUEST: i-dropout surveys similar to SDSS – IR-based survey: UKIDSS, (z=5.83), VISTA, allows detection up to z~8-9.

Quasar Density at z~6

• From SDSS i-dropout survey

– Density declines by a factor of ~40 from between z~2.5 and z~6

• Cosmological implication

– MBH~109-10 Msun – Mhalo ~ 1012-13 Msun – rare, 5-6 sigma peaks at z~6 (density of 1 per Gpc3)

• Assembly of supermassive BHs?

– The universe is only ~20 teddington

• ld, requiring non-stop Eddington

accretion of 100 Msun from z>>20 – Is Eddington-limited accrection from stellar seeds still permitted, or are alternative accretion modes (super-Eddington, intermediate mass BH) needed?

Fan et al. 2006

NV OI SiIV Ly a Ly a forest

• Rapid chemical enrichment in quasar vicinity
• Quasar env has supersolar metallicity : no metallicity evolution
• High-z quasars are old, not yet first quasars..

The Lack of Evolution in Quasar Emission Line Properties The Lack of Evolution in Quasar Emission Line Properties

Fan et al.2007

z~6 composite Low-z composite

Quasar Metallicity at z~6

Jiang, XF et al. 2007 near-IR spectroscopy: Gemini + VLT

Searching for Gunn-Peterson Trough

• Gunn and Peterson (1965)

– “It is observed that the continuum of the source continues to the blue of Ly-α ( in quasar 3C9, z=2.01)” – “only about one part of 5x106 of the total mass at that time could have been in the form of intergalactic neutral hydrogen ”

• Absence of G-P trough  the universe is still

highly ionized at z~6

Keck/ESI 30min exposure 

Gunn-Peterson Trough in z=6.28 Quasar

Keck/ESI 10 hour exposure 

White et al. 2003

Evolution of Lyman Absorptions at z=5-6

Δz = 0.15

Accelerated Evolution at z>5.7

• Optical depth evolution

accelerated

– z<5.7: τ ~ (1+z)4.5 – z>5.7: τ ~ (1+z)>11

– End of reionization?

• Dispersion of optical depth

also increased

– Some line of sight have dark troughs as early as z~5.7 – But detectable flux in ~50% case at z>6 – End of reionization is not uniform, but with large scatter

(1+z)4.5 (1+z)11 XF et al. 2006

Evolution of Ionization State

• UV Ionizing background:

– Assuming photoionization and model of IGM density distribution – UV background declines by close to an

• rder of magnitude from z~5 to 6.2

– Increased dispersion suggests a highly non-uniform UV background at z>5.8

• From GP optical depth

measurement, volume averaged neutral fraction increase by >~

• rder of magnitude from z~5.5 to

6.2

XF et al. 2006 Neutral fraction UV background

Reionization overlap at z~6-7?

• Comparing G-P observations

with high-resolution reionization simulation:

– Overlap redshift ~6.2 – Current simulation does not resolve earliest star formation to predict an accurate CMB polarization optical depth

Gnedin and Fan 2006

Evolution of Proximity Zone Size Around Quasars

• Size of Proximity Zone region

Rp ~ (LQ tQ / fHI )1/3

• Size of quasar proximity zone

decreases by a factor of ~2.4 between z=5.8 and 6.4 (Fan et al. 2006)

• Consistent with neutral fraction

increased by a factor of ~15 over this narrow redshift range

• Can be applied to higher z and fHI

with lower S/N data

• Actual size of proximity zone

dependent on details of radiative transfer and quasar model…

XF et al. 2006

Shapiro, Haiman, Mesinger, Wyithe, Loeb, Bolton, Haehnelt, Maselli et al.

Proximity zone size (Mpc) redshift

Dark Gap Distributions

• Dark gap statistics (Songaila & Cowie

2002)

– Gaps: regions where all pixels have τ >2.5

• Gaps among z~6 quasars

– Average length shows the most dramatic increase at z>5.8 → IGM is dominated by long, dark gaps

• Consistent with overlap at z~6-8?

– Dispersions

• Even at z>6, gap lengths are still

finite

• 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)

– Independent upper limit on neutral fraction

XF et al. 2006

Iye et al. 2006 Kashikawa et al. 2006

Ly α Galaxy LF at z>6

• Neutral IGM has extended GP damping wing → attenuates Ly α emission line
• New Subaru results

– Declining density at z~6-7 (2-3σ result) – Reionization not completed by z~6.5 – Neutral fraction could be as high as a few tenths but strongly model-dependent – cf. Malhotra & Rhoads, Hu et al.: lack of evolution in Ly α galaxy density

GRBs as Probes of Reionization

• Detected to z=6.30
• Advantages:

– Bright – Flat K-correction due to time dilation at high-z – 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: fHI < 0.6 (2- sigma) by fitting both DLA and IGM profiles

Damping wing?

GRB050904 Kawai et al. 2005

Probing Neutral Era

• 21cm probes:

– HI emission during reionization – 21cm Gunn-Peterson effects in high-z radio sources

• Metal absorption lines (Oh 2002, Becker et al. 2005)
• Lyα galaxy distributions (e.g. Malhotra and Rhoads); G-P gap distribution
• GRBs

Gnedin & Shiver McQuinn et al. Carilli et al.

What Ionized the Universe? AGNs or Galaxies

• Quasar LF at z~6:

– SDSS Wide: 7700 deg2, 17 quasars, zAB <20 – SDSS Deep: ~150 deg2, 6 quasars, 20<zAB<21 – AGES: 1 quasar in 5 deg2 at zAB<21.5

• Steeppening of LF:

– Φ∝ Φ∝L-3.1

– Comparing to Φ∝L-2.4 at z~4

Jiang, XF et al. 2007

SFR of galaxies Density of quasars

Reionization by AGNs?

• Can quasars do it?

– Too few quasars unless QLF remains to be steep to AGN luminosity

• Can low-luminosity AGNs

ionize the IGM by z~6?

– Stacking X-ray image of LBGs in UDF… too few faint AGNs

• Can accretion to seed BHs

ionize the IGM by z~15?

– Dijkstra, Haiman & Loeb (2004) – – Soft X-ray background Soft X-ray background

• verproduced
• verproduced

if quasars if quasars produce ~10 photons/H atom produce ~10 photons/H atom – – ‘ ‘Preionization Preionization’ ’ to to f f(HI)~50% (HI)~50% by X-rays is still allowed (e.g. by X-rays is still allowed (e.g. Ricotti Ricotti et al.) et al.)

Jiang, XF et al. 2007

Reionization Reionization by stellar sources? by stellar sources?

Necessary for reionization 6<z<9 (Stiavelli et al 2003)

• Large uncertainties in reionization photon budget:

– IGM clumpiness – UV radiation and escape efficiency – Large cosmic variance in deep field data – Galaxy luminosity function at high-z

Bouwens & Illingworth; Bunker et al.

Summary

• When?

– Reionization started early (z~10, WMAP) – And ended late (z~6, Gunn-Peterson); overlap at z~6-8

• How?

– History likely complex – Might not be a sharp phase transition in time

• feedback from galaxy formation

– Not homogeneous in space

• large scale structure
• What?

– Likely UV photons from star formation – Hard photons from accretion could still pre-ionize to low-level at high-z

Probing Reionization History

WMAP

21cm, GRB Planck, JWST