Search for Cosmic Hydrogen About half of horizon volume filled with HI, dominated by z>6 hi-z: lots out there, structures with up to 10 16 M סּ HI. Difficult to observe window, foregrounds. Mid-z: neutral HI in galaxies, 0.1 10 5 m 2 ). GMRT/SKA.
Image courtesy of NRAO/AUI and Chung et al., Columbia University
Traditional Radio Telescope Cost Drivers High Frequency: cryogenic receivers, surface, pointing accuracy Correlation/bandwidth: N 2 cost General purpose – steerable, reconfigurable HSHS target: $10/m 2, <1.4 GHz, transit Molonglo actual: $12/m 2, steerable cyl GMRT actual: $100/m 2, <1.4 GHz SKA target: $1000/m 2 VLA actual: $10000/m 2
HSHS: Large Area, Low Cost Surface: low frequency mesh (GMRT) Structure: passive transit cylinder Correlations: FFT is N log N instead of N 2 Signal processing: PC’s are $3/Gflop Astro-ph/0606104
Existing operational cylinders MOLONGLO 1600x12m Cost:$12/m 2 (current dollars) OOTY 530x30m Both rotate in one dimension Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney +
Cylinder History Popular 1960-1980 Lost favor with advent of cryogenically cooled pre-amplifiers. Room temp amplifiers with 20K noise temp now available. Illinois 400 ft Telescope ca. 1960
Local HI Luminosity Function Zwann et al at z=1.5 this is 30 microjansky We detect all these across 1/2 of sky in 6 months
Cosmic Magnification Cosmic shear has evolved as a direct way to map dark matter Several major surveys under way or planned – CFHTLS, LSST, SNAP Anticipated limitations: redshift distribution, PSF With redshifts, these limits can be overcome, and magnification is measured directly Measured through cross correlation in SDSS (Scranton et al 2005) Forecasts and models by Zhang and Pen (2005, 2006): overcomes intrinsic clustering.
Gravitational Lensing: increase flux, decrease density Magnification: increases number of bright galaxies, decreases faint ones.
Four Cylinders each 2 km long, 50m wide Line feeds at foci used to create 4000 beams N 2 km
CMU Prototype cylinders under construction. Funded by Seljak/Packard
Additional Science Find and monitor 1000s of new pulsars-- strongly constrain the gravity wave background Map galactic magnetic fields Study Early Ionization at z > 13
Pros and Cons of 21-cm Cylinder Scheme Off the shelf technology Low Cost Fast Constructions Expandable in area and field of view Expandable in Science Goal Astronomical Sources have clean signature Negligible 21 cm confusion 21 cm luminosity likely higher in the past Low Cost RFI unknown Intermodulation possible Cost not demonstrated 21 cm luminosity function at high z unknown
HI Evolution Major cost uncertainty is luminosity function evolution. Popular models differ by factor of several Effort under way to measure z=1.4 mass function using DEEP cross correlation (T. Chang, M. Davis, U. Seljak)
τ=0.09+/-0.03, z r =11 WMAP 3yr: rise of HI Cosmic precombination
White et al 2003: universe fully ionized at z<6
Reionization First objects: 21cm @ z=6-15 90-200 Mhz ΔT = 23 mK, ~μJy- mJy (up to 10 16 M סּ of HI) Angular scale 5’<Θ<30’, freq res 500 khz Challenging theory z=19-12 simulation, Iliev, Mellema, Pen 2005. 1 o FOV
Cosmic Reioniation Largest radiative transfer cosmological reionization simulations: 1 degree FOV. Detection in 21cm hyperfine transition with radio telescopes. Structure on large scales (>20’). Iliev, Mellema, Pen 2006
Foreground: Galactic Synchrotron Haslam 408 MHz Much brighter than signal, but no spectral structure
Detectability Luminosity proportional to object volume: bigger structures easier to find Noise dominated by galaxy: T=300(ν/150 Mhz) -2.5, higher frequency (lower redshift) much easier Mean emission challenging to discern (Gnedin and Shaver 2004). First targets: Stromgren spheres around bright quasars (Wyithe and Loeb 2004).
First Light Experiments Existing w/prelim data: PAST/21CMA (China), GMRT (India) Under construction: LOFAR (Netherlands), MWA (Australia), T-rex (Canada), CorE (Australia), VLA-VHF (USA) Future: SKA, JWST
Indian Giant Meterwave Radio Telescope 30 dishes @45m ea. Operates in 2m band Collaborators: Y. Gupta (chief scientist), Rajaram Nityananda (director), R. Subramanian, S. Sethi, A. Roshi (Raman), C. Hirata (IAS), T. Chang (UCB)
GMRT Search Operating telescope, 50000m 2, up to 32 Mhz BW, fully polarized, lowest band 100-200 Mhz. Biggest collecting area in this band. Half in central 1km core, rest in 50 km Y. Currently hits RFI limit after a few minutes of integration: power lines, TV stations, HAM amateurs, faulty home electronics. Exploration of new RFI mitigation schemes, software correlator, nearfield clean. Search for SDSS QSO Stromgren spheres in TV band: 6 antenna filters already replaced.
Power Line Noise Time-lag: Folded 70ms data on short baseline
CMB Comoving distances reionization Low l anomaly: model primary CMB to l~20 EoR ISW: lensing map predictions T-E correlations: can be predicted! Pen 2003
Potential Theoretical Benefits Precision measurement of power spectrum at 10 -8 accuracy (beyond PAST) Dark energy dynamics: q 0, a(t), ISW, dark matter dynamics/clustering (through lensing), gravity waves. Initial conditions: 2 nd order inflation effects, backreaction, curvature, etc. (through hydrogen matter P(k) and 3pcf).
Outlook Existing constraints: optical depth from WMAP, SDSS QSO’s. Theoretical progress: direct simulations indicate power on larger scales (>20’), making detections more tractable. current: initial data from Past/21CMA and GMRT, data analysis, ionospheric solution (Hirata). Several other experiments developing: LOFAR, VLA/VHF Bright outlook: several experiments underway or planned to tap the next cosmic horizon Exciting new window on universe for precision cosmology. Open field for theory and experiment.