Evolution and application of the 21 cm signal

throughout cosmic history

Jonathan Pritchard (CfA-HCO)

Collaborators: Steve Furlanetto (UCLA) Avi Loeb (Harvard) Mario Santos (CENTRA - IST) Alex Amblard (UCI) Hy Trac (CfA)

Renyue Cen (Princeton) Asantha Cooray (UCI)

2STScIMAR 2008 Overview

1. 21 cm as probe of high-z radiation backgrounds

2. Fluctuations in Ly andX-ray backgrounds lead to 21 cm fluctuations

3. What might 21 cm observations tell usabout first sources?

4. Reionization

5. Experimental prospects

z~30

z~12

z~7

3STScIMAR 2008 21 cm basics

•21 cm brightness temperature

•21 cm spin temperature

•Use CMB backlight to probe 21cm transition

z=13fobs=100 MHzf21cm=1.4 GHz

z=0

TS TbT

HITK

•3D mapping of HI possible - angles + frequency

•Coupling mechanisms: Radiative transitions (CMB) Collisions Wouthuysen-Field

10S1/2

11S1/2

n0

n1

n1/n0=3 exp(-h21cm/kTs)

•HI hyperfine structure

=21cm

4STScIMAR 2008 Wouthuysen-Field effect

Lyman

Effective for J>10-21erg/s/cm2/Hz/sr

Ts~T~Tk

W-F recoils 20P1/2

21P1/2

21P1/2

22P1/2

10S1/2

11S1/2 Selection rules: F= 0,1 (Not F=0F=0)

Hyperfine structure of HI

Field 1959

nFLJ

~21 cm

5STScIMAR 2008 Thermal History

e.g. Furlanetto 2006

6STScIMAR 2008 21 cm fluctuations

BaryonDensity

Gas Temperature

W-FCoupling

Neutralfraction

Velocitygradient

X-raysources

Lysources

ReionizationCosmology Cosmology

Brightnesstemperature

Amount ofneutral hydrogen

Spin temperature

Velocity(Mass)

b

7STScIMAR 2008 Angular separation?

•Anisotropy of velocity gradient term allows angular separation

Barkana & Loeb 2005

Bharadwaj & Ali 2004

BaryonDensity

Gas Temperature

W-FCoupling

Neutralfraction

Velocitygradient

•In linear theory, peculiar velocities correlate with overdensities

•Initial observations will average over angle to improve S/N

b

8STScIMAR 2008 Temporal separation?

BaryonDensity

Gas Temperature

W-FCoupling

Neutralfraction

Velocitygradient

X-raysources

Lysources

ReionizationCosmology Cosmology

Dark AgesTwilight

Brightnesstemperature

b

9STScIMAR 2008

Fluctuations from the first stars

dV

• Fluctuations in flux from source clustering, 1/r2 law, optical depth,… • Relate fluctuations in Ly and X-ray fluxes to overdensities

•Start with LyBarkana & Loeb 2005

Chen & Miralde-Escude 2006, Chuzhoy & Shapiro 2006, Pritchard & Furlanetto 2006,2007

• Three contributions to Ly flux: continuum & injected from stars + x-ray

continuum injected

10STScIMAR 2008Determining the first sources

Chuzhoy,Alvarez, & Shapiro 2006

Sources

Spectra

J,* vs J,X

S

Pritchard &Furlanetto 2007

bias source properties density

z=20

dominates

11STScIMAR 2008 X-ray heating

• Soft X-rays heat closer to source, hard X-rays have long m.f.p.

• X-ray flux -> heating rate -> temperature evolution• Integrated effect - so whole SF history contributes

Pritchard &Furlanetto 2007

12STScIMAR 2008 Indications of TK

TK<T

TK>T

• Learn about source bias and spectrum in same way as Ly • Constrain heating transition

T dominates

13STScIMAR 2008 X-ray background?

T x

?

• To avoid giving the idea of certainty…

Extrapolating low-z X-ray:IR correlation gives:Glover & Brand 2003

14STScIMAR 2008 Reionization

(100 Mpc/h)3 cube, 18803 particle N-body + UV photon ray tracing

X-ray heating and coupling included via simplemodel

Santos, Amblard, JRP, Trac, Cen, Cooray 2008

15STScIMAR 2008 Ionization history

Xi>0.1

zR~7~0.07

WMAP1WMAP3

WMAP5Zreion=10.8±1.4 (instant)Zreion~9 ±1.4 (extended)

16STScIMAR 2008 Theory vs Simulation

Furlanetto, Zaldarriaga, Hernquist 2004

• Bubbles imprint “knee” on large scales• Limited agreement at end of reionizationon large scales

17STScIMAR 2008 Experimental effortsLOFAR: NetherlandsFreq: 120-240 MHzBaselines: 100m-

100km

SKA: S. Africa/Australia ???Freq: 60 MHz-35 GHzBaselines: 20m-

3000km

MWA: AustraliaFreq: 80-300 MHzBaselines: 10m-

1.5km

PAST/21CMA: ChinaFreq: 70-200 MHz

Foregrounds are thebig problem!

More from Judd next

18STScIMAR 2008 Temporal evolution

Dark agesReionizationPost-reionization

Signal from denseneutral clumps at low z

Pritchard & Loeb 2008

19STScIMAR 2008 Temporal evolution

x T

?

MWA

SKA

20STScIMAR 2008 High-z Observations•Need SKA to probe these brightnessfluctuations

•Observe scalesk=0.025-2 Mpc-1

•Easily distinguishtwo models

•Optimistic foregroundremoval

•B~12MHz ->z~1.5

foregroundspoor angular resolution

21STScIMAR 2008 Low-z Observations

SKA

MWALOFAR

•Low k cutofffrom antennaesize

•Sensitivity ofLOFAR and MWA drops off by z=12

McQuinn et al. 2006

22STScIMAR 2008 Angular Separation

MWA SKA

LARC

Cosmology

Astrophysics

23STScIMAR 2008 Conclusions

• Today told a simple story - lots of uncertainty in all attempts at modeling this period

• Can use 21 cm to learn about the first luminous sources via the Ly background

• Temperature fluctuations should give insight into thermalevolution of IGM

• If X-ray heating important, then can learn about early X-ray sources

• Map out reionization topology and evolution• Detailed measurements will require SKA and luck• Beginnings of full theoretical framework coming into being• Early days for 21 cm and still unclear what will and will not be

possible - foregrounds will be determining factor

24STScIMAR 2008

Bonus material

25STScIMAR 2008 Redshift slices: Ly

•Pure Ly fluctuations

z=19-20

26STScIMAR 2008 Redshift slices: Ly/Tz=17-18

•Growing T fluctuationslead first to dip in Tb then to double peak structure

•Double peak requiresT and Ly fluctuationsto have different scaledependence

27STScIMAR 2008 Redshift slices: Tz=15-16

•T fluctuations dominate over Ly

•Clear peak-trough structure visible

• 2 <0 on largescales indicates TK<T

28STScIMAR 2008 Redshift slices: T/z=13-14

•After TK>T , thetrough disappears

•As heating continuesT fluctuations die out

29STScIMAR 2008 Redshift slices: /xz=8-12

•Bubbles imprint featureon power spectra once xi>0.2

•Non-linearities in density fieldbecome important

(TK fluc. not included)

30STScIMAR 2008 Thermal history

•Ly forest

Hui & Haiman 2003

•IGM retains short term memory of reionization - suggests zR<10•Photoionization heating erases memory of thermal history beforereionization

•CMB temperature

•Knowing TCMB=2.726 K and assuming thermal coupling byCompton scattering followed by adiabatic expansion allows informed guess of high z temperature evolution

??

Zaldarriaga, Hui, & Tegmark 2001

31STScIMAR 2008 Ionization history

Page et al. 2006

Becker et al. 2005

• WMAP3 measurement of ~0.09 (down from ~0.17)

• Gunn-Peterson Trough

•Universe ionized below z~6, some neutral HIat higher z•black is black

•Integral constraint on ionization history•Better TE measurements+ EE observations

32STScIMAR 2008 When did things start?

33STScIMAR 2008 Foregrounds

• Many foregrounds Galactic synchrotron (especially polarized component) Radio Frequency Interference (RFI)

e.g. radio, cell phones, digital radio Radio recombination lines Radio point sources

• Foregrounds dwarf signal: foregrounds ~1000s K vs 10s mK signal

• Strong frequency dependence Tsky-2.6

• Foreground removal exploits smoothness in frequency and spatial symmetries

• Cross-correlation with galaxies also important

34STScIMAR 2008 Reionization?

WMAP1WMAP3

WMAP5

=0.06 =0.09 =0.12

Zreion~11±1 (instant)

Zreion~9 ±1 (model)

35STScIMAR 2008 Global history

Heating

HII regions

IGM

expansion

Furlanetto 2006

Adiabaticexpansion

X-rayheating

Comptonheating

+ +

UV ionization recombination+

X-ray ionization recombination+

continuum injectedLy flux

•Sources: Pop. II & Pop. III stars (UV+Ly) Starburst galaxies, SNR, mini-quasar (X-ray)

•Parameters: fstar, X, N, Nion (+ spectra + bias +…)

36STScIMAR 2008 Angular Separation