Radio astronomy: Probing the Cosmic Reionization

Manchester, Oct 2007

Chris Carilli (NRAO)

Ionized

Neutral

Reionized

Chris Carilli (NRAO)

Berlin June 29, 2005

WMAP – structure from the big bang

Hubble Space Telescope Realm of the Galaxies

Dark Ages

Cosmic reionization

• Last phase of cosmic evolution to be explored

• Benchmark in cosmic structure formation indicating the formation of the first luminous objects.

• HI 21cm line is most direct, incisive probe of structure formation during, and process of, reionization.

• Radio(cm/mm) observations reveal the gas, dust, star formation, and AGN in the earliest galaxies

Constraint I: Gunn-Peterson Effect

Fan et al 2006

End of reionization?

f(HI) > 1e-3 at z = 6.3

f(HI) < 1e-4 at z= 5.7

Fan et al 2003

TT

TE

EE

Constraint II: CMB large scale polarization: Thompson scattering during reionization

Scattered CMBquad. => polarized

Horizon scale => 10’s deg

= 0.09+/-0.03 => zreion = 11+/-3

Page + 06

ESO

OI

Not ‘event’ but complex process, large variance: zreion ~ 14 to 6

Good evidence for qualitative change in nature of IGM at z~6

ESO

OI

Saturates, HI distribution function, pre-ionization?

Abundance?

3, integral measure?

Local ionization?

Geometry, pre-reionization?

Current probes are all fundamentally limited in diagnostic power

Need more direct probe of process of reionization = HI 21cm line

Local ioniz.?

Studying the pristine IGM into the EOR using redshifted HI 21cm observations (100 – 200 MHz)

Large scale structure:

cosmic density,

neutral fraction, f(HI)

Temp: TK, TCMB, Tspin

Heating: Ly, Xrays, shocks

)1()10

1)((008.0 2/1 δ +

+= HI

S

CMB fz

TT

Signal I: Global (‘all sky’) reionization signature in low frequency HI spectra

21cm ‘deviations’ < 1e-4 wrt foreground

Lya coupling: T_spin=T_K < T_CMB

IGM heating: T_spin=T_K > T_CMB

Gnedin & Shaver 03

Signal II: HI 21cm Tomography of IGM Zaldarriaga + 2003

z=12 9 7.6

δT_B(2’) = 10’s mK

SKA rms(100hr) = 4mK

LOFAR rms (1000hr) = 80mK

Signal III: 3D Power spectrum analysis

SKA

LOFAR

McQuinn + 06

δonly

δ + f(HI)

N(HI) = 1e13 – 1e15 cm^-2, f(HI/HII) = 1e-5 -- 1e-6

=> Before reionization N(HI) =1e18 – 1e21 cm^-2

Cosmic Web after reionization

Ly alpha forest at z=3.6 (δ < 10)

Womble 96

z=12 z=819mJy

130MHz

• radio G-P (=1%)

• 21 Forest (10%)

• mini-halos (10%)

• primordial disks (100%)

Signal IV: Cosmic web before reionization: HI 21Forest

• expect 0.05 to 0.5 deg^-2 at z> 6 with S_151 > 6 mJy

‘Pathfinders’: PAST, LOFAR, MWA, PAPER, …

MWA (MIT/ANU)LOFAR (NL)

PAST (CMU/China)

PAPER Berk/NRAO

Challenge I: Low frequency foreground – hot, confused sky

Eberg 408 MHz Image (Haslam + 1982)

Coldest regions: T = 100z)^-2.6 K

Highly ‘confused’: 1 source/deg^2 with S_0.14 > 1 Jy

Solution: spectral decomposition (eg. Morales, Gnedin…)

Foreground = non-thermal = featureless over ~ 100’s MHz

Signal = fine scale structure on scales ~ few MHz

10’ FoV; SKA 1000hrs

Signal/Sky ~ 2e-5

Cygnus A

500MHz 5000MHz

Simply remove low order polynomial or other smooth function?

‘Isoplanatic patch’ = few deg = few km

Phase variation proportional to wavelength^2

Solution: Wide field ‘rubber screen’ phase self-calibration

74MHz Lane 03

Challenge II: Ionospheric phase errors: varying e- content

TID

100”

-100”

Solution – RFI mitigation: location, location location…

100 people km^-2

1 km^-2

0.01 km^-2

First galaxies: ALMA/EVLA CO redshift coverage

Epoch of Reionization:

First galaxies: standard molecular transitions redshift to cm regime

•Total gas mass

•Gas dynamics

•Gas excitation

•High density gas tracers

First galaxies -- Radio astronomy into cosmic reionization

z ~ 6 QSO host galaxies: molecular gas and dust

• Giant reservoirs of molecular gas ~2e10 Mo = fuel for star formation.

• Currently: 2 solid detections, 2 likely at z~6

FWHM=350 km/s

z=6.42

Radio-FIR correlation

50K

Mdust ~ 1e8 Mo

Dust heating: star formation or AGN?

Follows Radio-FIR correlation: SFR ~ 3000 Mo/yr

VLA

PdBI

J1148+52: VLA imaging of CO3-2

Separation = 0.3” = 1.7 kpc

TB = 20K => Typical of starburst nuclei

rms=50uJy at 47GHz

Not just circumnuclear disk.

Mdyn~ 4e10Mo ~ Mgas >> Mbulge ~1e12 Mo predicted by M-

1” 5.5kpc

0.4”res

0.15” res

VLA imaging of gas at subkpc resolution

[CII] 158um ISM gas cooling line at z=6.4 30m 256GHz

Maiolino etal

CII PdBI Walter et al.

C+ = workhorse line for z>6 galaxies with ALMA

Structure identical to CO 3-2” (~ 5 kpc) => distributed gas heating = star formation?

SFR ~ 6.5e-6 L[CII] ~ 3000 Mo/yr

1”

CII + CO 3-2

Higher Density (>1e4 cm^-3) Tracers: HCN, CN, & HCO+,

HCO+ 1-0

• Linearly correlated with FIR => dense gas directly associated with star forming clouds• Lines 5-10x fainter than CO• ncr > 1e7cm^-3 for higher orders => higher order not (generally) excited?•Dense gas tracers best studied with cm telescopes

HCN 1-0

200uJy

Riechers

(sub)mm: high order molecular lines + fine structure lines

cm telescopes: low order molecular transitions

The need for collecting area: pushing to normal galaxies at high redshift -- spectral lines

cm: Star formation, AGN

(sub)mm Dust, molecular gas

Near-IR: Stars, ionized gas, AGN

Arp 220 vs z

The need for collecting area: continuum

A Panchromatic view of galaxy formation

Radio astronomy – Reionization and 1st galaxies

•‘Twilight zone’: study of first light limited to near-IR to radio wavelengths

• First constraints: GP, CMBpol => reionization is complex and extended: z_reion = 6 to 14

• HI 21cm: most direct probe of reionization

• Low freq pathfinders: All-sky, PS, CSS, Abs

• SKA: imaging of IGM

• First galaxies: cm/mm -- gas, dust, star formation, AGN

Signal VI: pre-reionization HI signal: ‘richest of all cosmological data sets’ eg. Baryon Oscillations (Barkana & Loeb)

Very difficult to detect !

z=50 => = 30 MHz

Signal: 30 arcmin, 50 mk => S_30MHz = 0.1 mJy

SKA sens in 1000hrs:

T_fg = 20000K =>

rms = 0.2 mJy

z=50

z=150

Destination: Moon!

RAE2 1973

No interference (ITU protected zone)

No ionosphere (?)

Easy to deploy and maintain (high tolerance electronics + no moving parts)

10MHz

Needed for probing ‘Dark ages’:

z>30 => freq < 50 MHz