The Square Kilometre Array A technology-enabled approach to `Hubble Volume’ Redshift Surveys A phased roll-out of an array that has seriously started (that will involve phased arrays).

Will only discuss the Cosmology & Galaxy Evolution Key Science Project See Carilli & Rawlings (2004) for everything else: Pulsars, GR & Gravitational waves Magnetic Universe Epoch of Reionisation Cradle of Life

Whether Dark Energy is Einstein’s Cosmological Constant Some important things that need both Planck and ‘Hubble Volume’ Redshift Surveys Whether Dark Energy is Einstein’s Cosmological Constant The neutrino (Hot Dark Matter) mass Whether the geometry of the Universe is precisely Spatially Flat (see Knox 2006)

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Need Redshift Resolution Geometric effects give systematic patterns in z for a given w Beware non-linearity/bias effects, at high k and low z Percival’s 2 evidence for w<-1 very exciting

Need multiple measures of P(k) mn= 0.05 eV mn= 0.25 eV mn=0.5 eV Z = 0.5 – 1 Z = 1.5 – 2 Z = 1 – 1.5 Abdalla & Rawlings (2007)

Some good things about radio methods Time coherence of electric field means 3D redshift surveys for free: photometric surveys lose information on k-modes parallel to the line-of-sight: loss of effective cosmic volume; loss of velocity-space distortion information that greatly aids marginalisation over galaxy bias Spatial coherence of electric field means a growing array can ‘zoom in’ to get direct (`rotation curve’) information on host dark- matter haloes Higher redshift maps to lower frequency, HI at 1.4 GHz at z=0 to ~300 MHz at z~4, collecting area becomes cheaper

State-of-the-art Verheijen et al. get ~10 objects to z~0.2 in ~200 h @ WSRT: Abell 963/2192

Technology and the Phased Approach Cosmic volume ~ (time) x (FOV) x (A/T)2 for radio HI If we rely on time, errors on P(k) improve by an order of magnitude every 100 years! Technology I: increase dish FOV by ~100 and `dedicate’ array, ~105 galaxies to z~0.2 (1% SKA pathfinders ~2010) Technology 2: increase A/T by ~10. ~107 galaxies over 20,000 deg2 to z~0.75 (10% SKA in dishes ~2015) Technology 3: Change in technology (500-800 MHz). Further increase in A/T and FOV. ~109 galaxies to z~2 (100% SKA in aperture arrays ~2020). Technology 4: Benefit from increased processing power as you integrate (300-800 MHz). >1010 galaxies to z~4 (2020-2030)

Phased and `All Digital’ Aperture Arrays Simulation by Michael Kramer (Manchester) Recent D&C exercise delivers 250 deg2 FOV!

Picture & Joke Credit: Paul Alexander The SKA on one slide processor Picture & Joke Credit: Paul Alexander

SKADS Universe in a Box Obreshkow et al, in prep. and Wilman et al, in prep.

Uncertain HI Evolution

Milestone 1: ~1% SKA (~2010) in ~100 days >105 galaxies: an ~1000 deg2 survey to z~0.2; gives P(k) and hence bias

Milestone 2: ~1% SKA+FMOS/AA ‘Radio stacking’ on optical/near-IR redshifts out to z~1 Wiggle-z: ~400 targets per deg2 over large (~30 deg2) patches: √12000~100 gain on star-forming subset of galaxies FMOS: 12,000 deg-2, √12000~100 gain on ALL galaxies in deg2 patches Should provide statistical detections of HI emission to z~1 (alongside HI absorption experiments to higher z)

Milestone 3: ~10% SKA (~2015) Dishes: >107 galaxies over ~20,000 deg2 to z~0.75 (or 800 MHz); multiple P(k) to z~0.35, stacked analyses to z~2 Likely to be similar cosmic volumes to optical redshift surveys (e.g WFMOS: combination very powerful for studying galaxy evolution and bias). Survey Volumes then grow, at best, linearly with t, hence P(k) accuracy grows as t0.5

Milestone 4: SKA (~2020) In ~100 days, phased arrays deliver >109 galaxies over ~20,000 deg2 to z~2 (and multiple P(k) to at least z~1)

SKA(100 days)+Planck

Measurement of Neutrino masses and hierarchies Abdalla & Rawlings (2007) If Smn is ~0.05 eV, SKA+Planck sufficient and necessary to measure it, and hierarchy must be normal If Smn > 0.25 eV, direct measurement of Nn too! With particle physics experiments, prospect of evidence for sterile neutrinos

SPARSE AA CRITICALLY- DISHES SAMPLED AA Milestone 5: SKA 2020-2030 ~300 MHz: HI at z~4 Aeff ~800 MHz: HI at z~0.75: ~day with dish-SKA to get multiple P(k): perfect because few x 365~20,000/30 ~500 MHz: HI at z~2: ~month with the AA-SKA to get multiple P(k): perfect because 10x12~20,000/250) SPARSE AA CRITICALLY- DISHES SAMPLED AA Frequency Collecting area below 500 MHz rises as (1+z)2 for sparse arrays, but only worth going to z~4 because of sky temperature (Braun 2006) Using multi-beaming to ‘shape’ FOV a (1+z)4 gives ~constant mapping speed, and a plausible FOV at the lowest frequency

Why? Curvature z~2-4 ruler z~1000 ruler

There are other strategies Gravitational lensing (e.g. LSST, JDEM, DUNE, SKA), Supernovae (e.g. JDEM) etc Overcoming systematics is the key: P(k)/BAO method seems to be accepted to be the cleanest, but get all measures of growth/geometry! For large-volume P(k)/BAO: brute-force replication is plausible or space (ADEPT?)