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: 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 “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 z=12 109MHz z=9 142MHz z= MHz   T B (2’) = 10’s mK => DNR > 1e5  LOFAR rms (1000hr) = 80mK  SKA rms(100hr) = 4mK Linear CDM Bubble dominated Galaxies

Pre-reionization HI signal, z > 15 or < 90GHz  Lunar imperative z=50 z=150 Barkana & Loeb Structure formation in linear regime in 3D Baryon acoustic oscillations imprinted at recombination (~ sound horizon at t recomb ) “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)

Very low frequency (<50MHz): pre-reionization HI signal 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

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 I: Ionospheric phase distortions

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 § 8 1) In the shielded zone of the Moon 31 emissions causing harmful inter­ference to radio astronomy observations 32 and to other users of passive services shall be prohibited in the entire frequency spectrum except in the following bands: a) the frequency bands allocated to the space research service using active sensors; 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 ) In frequency bands in which emissions are not prohibited by Nos 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)

Tsiolkovsky crater (100 km diameter) 20°S 129°E Apollo 15 Challenge: Low power super computing -- two weeks of darkness (LOFAR/Blue Gene = 0.15MW) Solution: polar regions, valleys of eternal darkness, peaks of eternal light = eternal power But how sharp is the knife’s edge?

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 DALI Science requirements Antennas/receivers Correlator Signal processing Communications Site selection Deployment/maintenance

$100M class EoR ground- based 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) DS2010: NRAO and reionization Destination Moon!

European Aeronautic Defence and Space Corporation/ASTRON (Falcke) Payload = 1000 kg (Ariane V) 100 antennas at 1-10 MHz ~ 1/10 SKA

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Current observations: z reion ~ 14 to 6 (Fan, Carilli, Keating 2006) Not ‘event’, but complex process, large variance time/space

Constraint I: Gunn-Peterson Effect Fan et al 2006 End of reionization?  f(HI) <1e-4 at z= 5.7  f(HI) >1e-3 at z= 6.3