epoch of reionization
Post on 07-Jan-2016
80 Views
Preview:
DESCRIPTION
TRANSCRIPT
Epoch of Reionization
•last phase of cosmic evolution to be explored
•bench-mark in cosmic structure formation indicating the first luminous structures
Cosmic reionization and other lunar radio studies
Chris Carilli (NRAO)
z=5.80
z=5.82
z=5.99
z=6.28
Large scale CMB pol: zEoR=11+/-3
First observational constraints on cosmic reionization
T
TE
EE
Gunn-Peterson Effect: zEoR >= 6
Fan
Page
TT
Current observations: zEoR = 14 to 6 (Fan, Carilli, Keating 2006)
Not ‘event’, but complex process, large variance time/space
GP => occurs in ‘twilight zone’, opaque _obs< 0.9 um
Limited Diagnostics
•GP: Ly > 1e4 for f(HI)> 1e-3 => low f(HI)
•CMB pol = integral measure of e => high f(HI)
Studying the pristine IGM into the reionization, and beyond: redshifted HI 21cm observations in range 30 – 200 MHz
SKA goal: Jy at 200 MHz Large scale structure: density, f(HI), T_spin
1e12Mo
1e9Mo
Lunar Advantage I: Interference
100 MHz z=13
200 MHz z=6
Destination: Moon!RAE-2 1973
• Ionospheric Opacity: p ~1 to 10 MHz
TIDs – ‘fuzz-out’ sources
‘Isoplanatic patch’ = few deg = few km
Phase variation proportional to ^-2
Solution: ‘Rubber screen’ phase self-calibration
Virgo A VLA 74 MHz Lane + 02
Lunar Advantage II: Ionospheric phase distortions
Remaining challenge: low frequency foregroundColdest regions: T = 100z)^-2.7 K
Highly ‘confused’: 3 sources/arcmin^2 with S_0.2 > 0.1 mJy
Eberg 408 MHz Image (Haslam82)
Solution: fitting in the spectral domain
HI 21cm Tomography of IGM Zaldarriaga + 2003
z=12 9 7.6
T_B(2’) = 10’s mK => DNR > 1e5
LOFAR rms (1000hr) = 80mK
SKA rms(100hr) = 4mK
1422+23 z=3.62 Womble 1996
N(HI) = 1e13 -- 1e15 cm^-2, f(HI/HII) = 1e-5 -- 1e-6
=> Before reionization N(HI) =1e18 – 1e21 cm^-2
Cosmic Web (IGM) after reionization = Ly alpha forest ( <= 10))
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 sources/deg^2 at z> 6 with S_151 > 6 mJy
z=12 z=8
GMRT 230 MHz – HI 21cm abs toward highest z radio AGN (z = 5.2)
S230 = 0.5Jy;
rms (20km/s) = 5 mJy
z(CO)
0924-2201 8GHz
1”
Van Breugel et al.
RFI = 20 kiloJy !
N(HI) < 1e20 (Ts/100) cm^-2
Only direct probe of host galaxy: dust, molecular gas
Coeval starburst/AGN: SFR ~ 1e3 Mo/yr
2e10 Mo of molecular gas = fuel for star formation
Early enrichment of heavy elements/dust: zsf > 8
J1148 VLA CO 3-2
2.5”
IRAM
Molecular gas + fine structure lines: J1148+5251 z=6.42
tuniv=0.87 Gyr[CII]
CO 6-5
1148+5251
Cosmic Stromgren Spheres
• 1148+5251: Accurate z_host from CO: z=6.419+/0.001
• Proximity effect: photons leaking from 6.32<z<6.419
•‘time bounded’ Stromgren sphere: R = 4.7 Mpc
• f(HI) = 1e-5 R^-3 (tqso/1e7) yrs
White et al. 2003
Loeb & Rybicki 2000
Largest ‘bubbles’ at end of reionization
HI imaging of Cosmic Stromgren spheres around z > 6 QSOs
0.5 mJy
LOFAR ‘observation’: 0.5 f(HI) mJy
Pathfinders: Set first hard limits on f(HI) at end of cosmic reionization
Easily rule-out cold IGM (T_s < T_cmb): signal = 360 mK
Wyithe et al. 2006
5Mpc
VLA-VHF: 180 – 200 MHz Prime focus X-dipole Greenhill, Blundell (SAO Rx lab); Carilli, Perley (NRAO)
Leverage: existing telescopes, IF, correlator, operations
$110K D+D/construction (CfA)
First light: Feb 16, 05
Four element interferometry: May 05
First limits: Winter 06
Project abandoned: Digital TV
KNMD Ch 9
150W at 100km
• Focus: EoR signal (power spec, CSS, abs)
• Very wide field: full cross correlation of all dipoles
• Staged engineering approach: GB Mileura07
PAPER: First images/spectra
Cygnus A
1e4Jy
Cas A 1e4Jy
3C392
200Jy
3C348
400 Jy
140MHz180MHz
Very low frequency (<30MHz): pre-reionization HI signal
Lunar imperative; eg. Baryon Oscillations (Barkana & Loeb)
Very difficult to detect
Signal: 10 arcmin, 10mk => S_30MHz = 0.02 mJy
SKA sens in 1000hrs:
T= 100(/200 MHz)^-2.7 K
= 20000K at 30MHz =>
rms = 0.2 mJy
Need > 10 SKAs
Need DNR > 1e6
z=50
z=150
Lunar VLF science: 0.1 to 10 MHz
Advantages
• Between Earth’s ionospheric cutoff and heliosphere/Galactic free-free cutoff
•Blocked from earth auroral emission
•RFI Protected ‘volume’ (ITU 22.22 – 22.25)
•Easy deployment: Javelins, Roll-out, Rover, Inflatables
•Easy maintenance: ‘cheap’, high tolerance electronics, no moving parts
VLF science
Coronal Mass Ejections and space weather: ‘early warning system’ – passive + remote sensing (Bastian)
Extrasolar planetary radio bursts (Lazio)
~ 1 – 100 MHz
S ~ 0.1 – 100 mJy
Array of lunar sensors (Falcke/ASTRON)
Moon as a neutrino detector: Cherenkov radiation from neutrinos in lunar regolith
Geophones: lunar seismology
•IPS/ISS angular/temporal broadening: 1MHz => 1deg, 5years
•Faraday rotation => no linear polarization
•High sky temperature
•Low power super computing: LOFAR/Blue Gene = 0.15MW
•Diffraction limit: how sharp is ‘knifes edge’?
•Lunar ionosphere: p = 0.2 to 1MHz (LUNA19,20 1970’s)?
Very low frequencies (<10MHz): Lunar challenges
ALMA on the moon: Why?
• No Troposphere – phase and opacity, eg. 650GHz (350m): Trx = 125K, =0.5, Tsky=150K => Same sensitivity with 16 ants vs. 64
• No wind, less gravity: lighter dishes
• Stable platform for interferometry
Why not?• Cryogenics: need 4K (HeII) for SIS
• Power: ALMA = 5-8 MW
5000m
Radio astronomy – Probing Cosmic Reionization
•First constraints: GP, CMBpol=> zEoR = 6 to 14
• HI 21cm: most direct probe of reionization
•Low freq pathfinders:
All-sky, PS, CSS, Abs.
•SKA: imaging of IGM
• Lunar advantages:
Interference
No ionosphere
Relatively ‘easy’
European Aeronautic Defence and Space Corporation/ASTRON (Falcke)
• Payload = 1000 kg (Ariane V)
• 100 antennas at 1-10 MHz ~ 1/10 SKA
END
All sky: SI deviations = 0.001
Solution: spectral decomposition (eg. Morales, Gnedin…)
10’ FoV; SKA 1000hrs
Power spectral analysis: Fourier analysis in 3D – different symmetries in freq space (ie. Different spectral chan-chan correlation)
Freq
Signal Foreground
Solution – RFI mitigation: location, location location…
100 people km^-2
1 km^-2
0.01 km^-2
‘Pathfinders’: PAST, LOFAR, MWA, VLA-VHF, …
MWA prototype (MIT/ANU)
LOFAR (NL)
PAST (CMU/China) VLA-VHF (CfA/NRAO)
Main Experiment: Cosmic Stromgren spheres around z=6 to 6.5 SDSS QSOs (Wyithe & Loeb 2004)
VLA-VHF 190MHz 250hrs
15’
20 f(HI) mK
0.50+/-0.12 mJy
VLA spectral/spatial resolution well matched to expected signal: 7’, 1000 km/s
Set first hard limits on f(HI) at end of cosmic reionization (f(HI) < 0.3)
Easily rule-out cold IGM (T_s < T_cmb): signal = 360 mK
LOFAR Hi-Band Antenna (110-240 MHz)LOFAR Hi-Band Antenna (110-240 MHz)
Westerbork Westerbork Radio Radio
ObservatoryObservatory
Paradigm shift: from steel to silicon.
Past: a lot of steel to focus radiation on a single electronic receiver
Future: many digital receivers and massive data processing synthesize virtual telescope in software
ARTICLE 22(ITU Radio Regulations)
Space servicesSection V – Radio astronomy in the shielded zone of the
Moon22.22 § 8 1) In the shielded
zone of the Moon31 emissions causing harmful inter ference to radio astronomy observations32 and to other users of passive services shall be prohibited in the entire frequency spectrum except in the following bands:
22.23 a) the frequency bands allocated to the space research service using active sensors;
22.24 b) the frequency bands allocated to the space operation service, the Earth exploration-satellite service using active sensors, and the radiolocation service using stations on spaceborne platforms, which are required for the support of space research, as well as for radiocommunications and space research transmissions within the lunar shielded zone.
22.25 2) In frequency bands in which emissions are not prohibited by Nos. 22.22 to 22.24, radio astronomy observations and passive space research in the shielded zone of the Moon may be protected from harmful interference by agreement between administrations concerned.
22.22.1 The shielded zone of the Moon comprises the area of the Moon’s surface and an adjacent volume of space which are shielded from emissions originating within a distance of 100 000 km from the centre of the Earth.
32 22.22.2 The level of harmful interference is determined by agreement between the administrations concerned, with the guidance of the relevant ITU-R Recommendations.
Good “news” …The Moon is radio protected!
The back side of the moon is declared as a radio protected site within the ITU Radio Regulations
The IT Radio Regulations are an international treaty within the UN.
Details are specified in a published ITU Recommendation (this is a non-mandatory recommendation, but is typically adhered to).
Radio astronomy on the moon has been a long-standing goal, protected by international treaties!
Steps need to be taken to protect the pristine and clean nature of the moon.
Lunar communication on the far side needs to be radio quiet.
Lunar LOFAR:Distributed array of radio sensors
Start with N=100 antennas Collecting area:
Aeff=N2/8 (3 MHz; ~100 m)Aeff~ 0.125 km2
(17 football fields or ~400 m dish) First prototype phase:
Antennas, power, computers, communication, dispatcher
Weight ~1000 kg (payload) Needs only one Ariane V launch
Separation D = 1 km → 1000 km Resolution (/D):
~1.6° (D=1 km, 10 MHz) ~6’’ (D=1000 km, 10
MHz) ~ 1’ (D=1000 km, 1
MHz )• Remote antennas are added later
Ionosphere Opacity:
p ~ 1 to 10MHz
Phase errors
TIDs – ‘fuzz-out’ sources
‘Isoplanatic patch’ = few deg = few km
Phase variation proportional to wavelength^2
Global reionization signature in low frequency HI spectra
(Gnedin & Shaver 2003)
double
fast21cm ‘deviations’ at
1e-4 wrt foreground
Spectral index deviations of 0.001
top related