lunatic fringe: probing the dark ages from the dark side of the moon c. carilli (nrao) enchanted...
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Lunatic fringe: probing the dark ages from the dark side of the MoonC. Carilli (NRAO)
Enchanted Skies
Socorro, NM
Sept. 2008
Dark Ages
Twilight Zone
Epoch of Reionization
• Last phase of cosmic evolution to be tested • Bench-mark in cosmic structure formation indicating the first luminous structures
Dark Ages
Twilight Zone
Pushing into reionization: most distant galaxies and quasars
SDSS J1148+5251
tuniv ~ 0.87 Gyr
First constraints on cosmic reionization • Gunn-Peterson Effect toward z~6 QSO = absorption by the neutral intergalactic medium (IGM) at tuniv < 1Gyr
Fan et al 2006
0.87 Gyr
1.0
• From tuniv ~ 0.87 to 1.0 Gyr, neutral fraction changes by order of magnitude
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Gnedin 03
Reionization: the movie
8Mpc comoving
Radio => Hydrogen Gas
Most direct probe of the neutral IGM during, and prior to, cosmic reionization, is the 21cm line of neutral hydrogen
HI spin flip => 21cm radiation (1420 MHz)
3D ‘tomography’ of the evolution of the large scale structure of the IGM: “richest of all cosmological data sets” (Loeb)
Low frequencies: Universal expansion (‘redshift’) implies HI 21cm line will be observed at < 200 MHz
Weak signal requires very large area telescopes ‘Square kilometer array’
400Myr, 109MHz 600Myr, 142 MHz 800Myr, 178MHz
Challenge I: Low frequency foreground – hot, confused sky
Eberg 408 MHz Image (Haslam + 1982)
Cosmological signal ~ 0.00001 x Sky
Fluctuations in ionospheric electron content causes interferometric phase errors at low radio frequencies ~ ‘radio seeing’
Challenge II: Ionospheric ‘seeing’
Virgo A 6 hrs VLA 74 MHz Lane + 02
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15’
Challenge II: Ionospheric ‘seeing’
Challenge III: Interference
100 MHz z=13
200 MHz z=6
Solutions -- RFI Mitigation (Ellingson06)
Digital filtering: multi-bit sampling for high dynamic range (>50dB)
Beam nulling/Real-time ‘reference beam’
LOCATION!
VLA-VHF: 180 – 200 MHz Prime focus CSS search Greenhill, Blundell (SAO); 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 06/07
Murchison widefield array (MIT - Melbourne)
Precision Array to Probe the Epoch of Reionization
(Berkeley -- NRAO)
Radio astronomers going to the ends of the Earth
Long History of Lunar Low Freq Telescope
Gorgolewski 1965: Ionospheric opacity
• Ionosphere opaque below 10 MHz
• Interstellar medium opaque below 0.1 MHz
• tuniv < 10Myr => not (very) relevant for HI 21cm studies, ‘beyond dark ages’
Lunar window
ion. cutoff ~ 30m
ISM cutoff ~ 3km
Return to moon is Presidential national security directive (an order, not a request).
Summary of STScI Workshop, Mario Livio, Nov. 2006
“The workshop has identified a few important astrophysical observations that can potentially be carried out from the lunar surface. The two most promising in this respect are:
(i) Low-frequency radio observations from the lunar far side to probe structures in the high redshift (10 < z< 100) universe and the epoch of reionization
(ii) Lunar ranging experiments…”
Ares IAres I Ares VAres V
Ares V
• 10m diameter faring
• Lifting power = 65 tons to Moon
Heavy lifting: capitalize on future launch vehicles
Clementine (NRL) star tracker
Lunar advantage I: ultra-thin ionosphere Soviet LUNA orbiters in 1970’s detected plasma layer > 10 km above surface Apollo surface+subsatellite: detected photoionized layer extending to 100km p = 0.2 to 1 MHz
large day/night variation => two weeks of ionosphere-free night-time
Advantage II: Interference
Lunar shielding of Earth’s auroral emission at low freq (Radio Astronomy Explorer 1975)
Alexander + 1975
12MHz
The Moon is radio protectedARTICLE 22
(ITU Radio Regulations)Space services
Section V – Radio astronomy in the shielded zone of the Moon
22.22 § 8 1) In the shielded zone of the Moon31 emissions causing harmful interference 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.
Other advantages
• Easier deployment: robotic or human
• Easier maintenance (no moving parts)
• Less demanding hardware tolerances
• Very large collecting area, undisturbed for long periods (no weather, no animals, not many people)
Deployment
• Javelin
• ROLS: polyimide circuit-imprinted film
• Dipoles: robotic with rover
• Dipoles: manually
Array of lunar sensors (Falcke)
• ‘Lunar internet’
• Cherenkov radiation from neutrinos passing through the lunar regolith
• Geophones: lunar seismology
Apollo 15
• Array data rates (Tb/s) >> telemetry limits, requiring in situ processing, ie. low power super computing (LOFAR/Blue Gene = 0.15MW)
• RFI shielding: How far around limb is required?
• Thermal cycling (mean): 120 K to 380 K
• Radiation environment
• Regolith: dielectric/magnetic properties
Lunar challenges
Lunar shielding at 60kHz
Takahashi + Woan
Tsiolkovsky crater
(100 km diameter)
20°S 129°E
Apollo 15But how sharp is the knife’s edge?
Energy solutions: polar craters of eternal darkness, peaks of eternal light = eternal power
DALI - LAMA: A path to enlightenment
NASA funded joint design study
• Dark Ages Lunar Interferometer (Lazio)
• Lunar Array for Measuring 21cm Anisotropies (Hewitt)
Science (Loeb, Furlanetto)
Science requirements (Carilli, Taylor)
Antennas (Bradley, MacDowall)
Receivers (Backer, Ellingson)
Correlator (Ford, Kasper)
Data communication (Ford, Neff)
Site selection (Hoffman, Burns)
Deployment (de Weck, DeMaio)
Engineering: power/mech/therm
Goal: Decade Survey 2010 white paper with mission concept, (rough) costing, and technological roadmap
2010 -- 2020: technology development
<2010: mission concept study
2020 -- 2025: Design/Fabrication/Test
2026+: operations
Interim programs
•Orbiter: RFI, ion
• First dipoles: environ., phase stability
• Global signal
Very long range planning!
European Aeronautic Defense and Space Corporation/ASTRON (Falcke)
• Payload = 1000 kg (Ariane V)
• 100 antennas at 1-10 MHz ~ 1/10 SKA
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Say, its only a PAPER moonSailing over a cardboard seaBut it wouldn't be make-believeIf you believed in me
CMB large scale polarization -- Thomson scattering during reionization
Scattering => polarized
Large scale: horizon scale at reionization ~ 10’s deg
Signal is weak: only 1% of T
=> finite ionization persisting to tuniv ~ 0.4Gyr
Page et al. 2006
Combined CMB + GP constraints on reionization
Not ‘event’ but complex process, large variance in space and time, starting ~ 400 Myr after Big Bang, ending ~ 800 Myr after BB.
Combined CMB + GP constraints on reionization
Current probes are all fundamentally limited in diagnostic power: Need more direct probe of process of reionization
The amazing and EXPANDING universe
3/13/22 ;)(2
1 −∝∝=>= tdtdR
tRR
GMmdtdR
m
Contents of the Universe:
•70% Dark Energy
•27% Dark Matter
•3% Baryons
PAPER: Staged Engineering• Broad band sleeve dipole + flaps
• 8 dipole test array in GB (06/07) => 32 station array in WA (2008) to 256 (2009)
• FPGA-based ‘pocket correlator’ from Berkeley wireless lab: easily scale-able
• S/W Imaging, calibration, PS analysis: AIPY + Miriad/AIPS => Python + CASA, including ionospheric ‘peeling’ calibration
100MHz 200MHz
BEE2: 5 FPGAs, 500 Gops/s