HI 21cm Tomography of IGM: freq ~ 100 to 200 MHz Furlanetto, Zaldarriaga + 2004 z=12 9 Large scale structure: , f(HI) , Temp (K, CMB, Spin) Advantages: 3D, optically thin, dominant baryon component Tomography requires SKA TB(2’) = 10’s mK SKA rms(100hr) = 4mK LOFAR rms (1000hr) = 80mK 0.5Mpc 7.6

Challenge: Low frequency foreground – hot, confused sky Eberg 408 MHz Image (Haslam + 1982) 0.5 to 5.0 GHz Coldest regions: T ~ 100 (/200 MHz)^-2.6 K Highly ‘confused’: 1 source/deg^2 with S140 > 1 Jy Synch. smooth ~ 100MHz vs. 21cm lines ~ 1 MHz

Chromatic aberration: Frequency differencing with MHz channels doesn’t work well due to frequency dependent far-out sidelobes 142, 174 MHz

Simulation: effects of residual calibration errors 6C source counts > 1Jy (Smax = 200 Jy)

UVSUB ~ ‘real-time’ source removal IMLIN ~ post-processing freq fitting (3rd order)

Datta+ 09 0.1% 1% For errors constant over 1 day: DNR requirement ~ 0.2% calibration errors

Datta + Bowman in prep 300 hours 0.1% calibration errors

Cosmic Stromgren Sphere Accurate host redshift from CO: z=6.419+/0.001 Ly a, high ioniz lines: inaccurate redshifts (z > 0.03) Proximity effect: photons leaking from 6.32<z<6.419 White et al. 2003 z=6.32 ‘time bounded’ Stromgren sphere: R = 4.7 Mpc tqso = 1e5 R^3 f(HI)~ 1e7yrs or f(HI) ~ 1 (tqso/1e7 yr)

Loeb & Rybicki 2000

CSS: Constraints on neutral fraction at z~6 Nine z~6 QSOs with CO or MgII redshifts: <R> = 4.4 Mpc (Wyithe et al. 05; Fan et al. 06; Kurk et al. 07) GP => f(HI) > 0.001 If f(HI) ~ 0.001, then <tqso> ~ 1e4 yrs – implausibly short given QSO fiducial lifetimes (~1e7 years)? Probability arguments + size evolution suggest: f(HI) > 0.05 Wyithe et al. 2005 Fan et al 2006 P(>xHI) 90% probability x(HI) > curve =tqso/4e7 yrs