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