Saleem ZaroubiKapteyn Astronomical Institute

University of Groningen

The Universe's Epoch of Reionization

Overview

The Astrophysics of Reionization: What do we know?What don't we know?

Reionization sources Probes of Reionization The the 21 cm emission from the LOFAR-

EoR experiment. Summary

Credit for picture: WMAP team

Epoch of Reioinzation

What do we know?

The Lyman-alpha forest: At z<6 the Universe is ionized

The Universe has completed its ionization by redshift 6: SSDS quasars

The WMAP polarisation measurement suggest that ionization has happened at about z~10.

How do we know the Universe is ionized

The Lyman-α Forest Along DistantQuasar Spectra (tUniverse~1 Billion yr)

QSO 1422+23, zem=3.62, S/N~150

At z ~ 4 the IGM is 10-4 neutral

n=1

n=2n=3n=4

1216 Å

Lyman-seriestransitions

Becker et al. 01 and Djorkovski et al. 01, and Fan et al. (02 & 04) have detected sudden increase in the flux decrement bluewards of the Lyman-α emission of QSO spectra at z~6. This sharp increase indicates the observation of the “tail” of the reionization process.

The Sloan Quasars

CMB Polarization

E

Electron scattering

Incoming Electromagnetic Field Same Flux

↓

No preferred Polarization

Different Fluxes

↓

A preferred Polarization

z ~ 1100

Ionized UniverseNeutral Universe

Z=0

Ioni

zed

& H

ot U

nive

rse

WMAP 5 Year data

c t ~

1o

Horizon Scale at Recombination

τ ~0.09

What don’t we know?

When did the reionization happen? What are the sources of ionizing radiation?

Stars, miniqsos, decaying DM, exotic physics,…

How fast did it spread and in what fashion? How did the reionization influence the

subsequent galaxy and structure formation in the Universe?

Sources of ionization

● Stars: PopIII and PopII● Miniqsos● Decaying Dark Matter

particles (WIMPs)● Other exotic physics

(decaying cosmic strings)

Abel et al., 2000, 2002, Bromm et al. 2002, Furlanetto et al. 2004, Furlanetto and Loeb 002, Madau et al. 1997, Mellema et al. 2006, Nusser 2005, Ricotti and Ostriker 2004a,b, Thomas et al. 2009, Thomas and Zaroubi 2008, Zaroubi and Silk 2005, Zaroubi et al. 2008.

Form favourably very massive stars very early on. – First stars are different creatures from the ones

we see in the local universe (no metals). – Atomic cooling is efficient in halos with Tvir>104k

(~109Msun). At smaller masses H2 cooling probably produces very massive stars.

– Efficiency of producing stars!! In our environment the main question is why star formation is so inefficient.

Abel, Bryan, Norman 00., Bromm Larson 00

Possible ionization sourcesThe first stars

Possible ionization sources

Black holes as sources (x-ray). – At z~6 we observe black holes with 109Msun

Other physics: – Decaying DM particles – Decaying string loops.– ....

Simulations

• Most simulations assume stellar ionization sources.

Ciardi & Ferrara.

Gnedin

Cen et al.

Mellema et al.

Khan et al.

and many others

Iliev et al. 07

Possible decoupling sourcesThe first massive black holes

BHs with intermediate masses (103-6Msun) could ionize the Universe and heat it up.

Thomas & Zaroubi 07

~3 Mpc comoving

Quasars with Black-hole masses of ~109Msunare seen at z~6.7

Possible Histories

Thomas et al.2008

Probes of Reionization

Background radiation: CMB, X-ray, IR High redshift galaxies Lyman-alpha emitters High redshift QSOs (Lya forest, bubbles,...) Most promising: the redshifted 21 cm Most promising: the redshifted 21 cm

from neutral hydrogen. from neutral hydrogen. 21 cm forest21 cm forest (provided intense sources are

available)

The 21 cm transition

• The 21 cm hyperfine transition is a forbidden transition between the two 12s1/2 ground level states of hydrogen.

• The relative population of the two states is given, n1/n0=g1/g0 exp(-T*/Ts) with Ts (the spin temp.) and T*=0.068 k

• The value of the Ts is given by:n0, g0

n1, g1

21 cm

Ts =TCMB + y®Tk + ycTk

1 + y® + yc Field 1958

Lyman-alpha Coupling

• The Wouthuysen-Field effect, also known as Lyman-alpha pumping.

Dominant in both in the case of stars & Black-holes, due to photo and collisional excitations, respectively.

Collisional Coupling

H-H collisions that excite the 21 cm transition. This interaction proceeds through electron exchange.

H-e collisions. Especially important around primordial X-ray sources (mini-quasars).

– This effect might also excite Lyman-alpha transition which adds to the Ts- TCMB decoupling efficiency.

Chuzhoy et al. 06

Zaroubi et al. 06

The brightness temperature: The measured quantity

The quantity that is measured with radio telescopes along a given line of sight and is given by:

The sources that ionize are probably the same as the ones that decouple

±Tb ¼ 28mK(1 + ±)xHITs ¡ TCMB

Ts

­bh2

0:02

·0:24

­m

µ1 + z

10

¶¸12

The Global evolution of the Spin Temperature

At z~10 Ts is tightly coupled to TCMB. In order to observe the 21 cm radiation decoupling must occur.

Quasars and X-ray radiation

• Assume BH mass & SED • Solve for neutral fraction as a function

of distance. • Calculate the kinetic, spin & brightness

temp.

Kuhlen, Madau & Montgomery 06

Zaroubi et al. 2006

The signal: Stars vs. Miniqsos

Thomas & Zaroubi 2008

The Signal:Quick and dirty simulations

Thomas et al. 2008

Simulations-ionizations with QSOs or stars

Thomas et al. in prep.

Quasars

Stars

LOFAR and the Epoch of Reionization

Currently there are a number of instruments developed in the world to detect the EoR, LOFAR, MWA, 21CMA, SKA.

LOFAR is a radio telescope (interferometer) with software correlator.

LOFAR will have many astronomical and non-astronomical uses.

Astronomy: LOFAR will have 5 key projects.– Epoch of Reionization– Deep Extragalactic Surveys– Transient Sources– Ultra-High Energy Cosmic Rays– Galactic Magnetism

LOFAR Tiles

100 Low Band Antenna’s

Optimized for 30-80 MHz

100 High Band Tiles 4x4 antenna’s Optimized ~115-240

MHz

Low Band Antenna

High Band Antenna

The Observationat z=6-11.5

EoR signal

Foregrounds

Ionosphere

Telescope

RFICorrelatorBluegene

LOFAR – The Instrument & RelevantRequirements for the EoR KSP

o Frequency 115 – 205 MHz range: (30MHz settings of 195 subbands)

o Spectral 1 KHz within sub-band (RFI excision) resolution: 10 KHz for storage (dt=10 sec)

100 KHz for analysis

o HBA station: 50 tiles (4x4 dua pol. dipoles) 30 m diameter station

o Sensitivity: rms=500 mK after 3 hrs (core; ΔΘ~3-5') (Δν=1MHz) rms= 50 mK after 300 hrs.

Radio Interferometers

Time delay=L/c

The EoR key project:Scientific goals

The plan is to statistically measure the EoR signal and as the data collection proceeds to refine our measurement and produce a full power spectrum.

The environment of very high z quasars. Cross correlate with other data sets:

– CMB (Planck data).– Lyman-alpha emitters .– Other complementary data.

The 21 cm forest (if a strong enough background source is found).

Galactic foreground

• SYNCHROTRON EMISSION (~70%)SYNCHROTRON EMISSION (~70%)

SOURCES:SOURCES: electrons trapped in the magnetic electrons trapped in the magnetic fields of discrete galactic supernovae remnants and fields of discrete galactic supernovae remnants and diffuse emission from interaction of cosmic-ray diffuse emission from interaction of cosmic-ray electronselectrons with with galactic magnetic field galactic magnetic field

DIFFUSE SYNCHROTRON EMISSIONDIFFUSE SYNCHROTRON EMISSION

Spectrum is close to a featureless power law with a smooth variation in spectral index.

average spectral index (100 MHz) b=-2.55, with position dispersion s(b)~0.1 (Shaver et al. 1999)

SUPERNOVAE REMENANTSSUPERNOVAE REMENANTS

• Free-Free emission (1%)Free-Free emission (1%)

Exrta-galactic foreground

• Radio galaxies (AGNs, starburst etc.)Radio galaxies (AGNs, starburst etc.)

― based on radio sky simulations by Jackson et al. 2005

― 3 TYPES OF SOURCES: FRI, FRII (Fanaroff & Riley 1972) & star forming (SF) galaxies

• Galaxy ClustersGalaxy Clusters― The Hubble Volume Simulation Cluster Catalogue (Virgo Consortium, 2002)―DMH Mass – Xray correlation (Jenkins et al., 2001) ― X ray – radio luminosity correlation (Enβ lin & Röttgering, 2002). 30% with radio properties.― Redshift, virial radius ⇒ angular size ― Spectral index distribution from Cohen et al. 2004

The signal + Foregrounds

Jelic et al. 2008

Tomography of the Reionization Process: What will we learn?

The dark ages: Fluctuations PS at z~10.(Non)-Gaussianity, Universe’s Geometry (AP test).P

re

o First objects and their properties.

o How fast and in what fashion did reionization spread.D

uri

ng

Influence on subsequent galaxy and structure formation in the UniverseP

ost