Probing the dark ages with a
lunar radio telescope
Chris Carilli, Feb 2008
Dark Ages
15 < z < 200
Reionization
6 < z < 15
•last phase of cosmic
evolution to be explored
• Reionization: 100 MHz
to 200 MHz, HI 21cm
signal being explored by
‘path-finders’
•Dark ages: < 100 MHz.
HI 21cm signal is the
only method for probing
structure formation into
Dark Ages. VLF =>
possible lunar
imperative?
Return to moon is Presidential
executive order, not request
(national security directive)
A brief summary of highlights
from the STScI Workshop,
M. 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…”
HI 21cm Tomography of IGM
Zaldarriaga + 2003
z=12 109MHz
Linear CDM
z=9 142MHz
z=7.6 165MHz
Bubble
dominated
TB(2’) = 10’s mK => DNR > 1e5
LOFAR rms (1000hr) = 80mK
SKA rms(100hr) = 4mK
Galaxies
Pre-reionization HI signal, z > 15 or  < 90GHz  Lunar
imperative
Barkana & Loeb
• Structure formation in linear
regime in 3D
• Baryon acoustic oscillations
imprinted at recombination (~
sound horizon at trecomb)
•“Richest of all cosmological
data sets” -- Better than the
CMB (1e16 pixels vs 1e7
-- Three dimensional
-- Not limited by silk damping
(photon-diffusion; l > 700)
z=50
z=150
Very low frequency (<50MHz): pre-reionization HI signal
Very difficult to detect
 Signal: 10 arcmin, 10mk => S30MHz = 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
Lunar Advantage I: Ionospheric phase distortions
• Ionospheric Opacity:
p ~1 to 10 MHz
 TIDs – ‘fuzz-out’
sources
‘Isoplanatic patch’ =
few deg = few km
 Phase variation
proportional to ^-2
Virgo A VLA 74 MHz Lane + 02
Lunar advantage II:
terrestrial interference
shielding
Good “news” …
The Moon is radio protected!
ARTICLE 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
• High-tolerance electronics
• Easier maintenance (no moving
parts)
Accepted NASA proposals for
design concepts
• Lunar Array for Radio Cosmology
(Hewitt et al.)
• Dark Ages Lunar Interferometer
(Lazio etal.)
• Joint effort to produce white paper
for DS2010
Science requirements
Antennas/receivers
Correlator
Signal processing
Communications
Site selection
Deployment/maintenance
DALI
2020
2030
Destination Moon!
DS2010: NRAO and
reionization
• $100M class EoR groundbased telescope will be
proposed (by whom?)
• lunar array study likely to be
proposed
• Will NRAO be involved in
major way?
(Are dipole arrays better than dishes
at 150 MHz: EVLA correlator + E
array has tremendous potential for
reionization)
European Aeronautic Defence and Space Corporation/ASTRON (Falcke)
• Payload = 1000 kg (Ariane V)
• 100 antennas at 1-10 MHz ~ 1/10 SKA
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
END
Current observations: zreion ~ 14 to 6 (Fan, Carilli, Keating 2006)
Not ‘event’, but complex process, large variance time/space
Constraint I:
Gunn-Peterson
Effect
End of reionization?
f(HI) <1e-4 at z= 5.7
f(HI) >1e-3 at z= 6.3