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Rise and Fall of HI

Rise and Fall of HI. Ue-Li Pen 彭威礼. Radiative Xfer simulation by Iliev, Mellema & Pen. Jeff Peterson, CMU. Search for Cosmic Hydrogen. About half of horizon volume filled with HI, dominated by z>6

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Rise and Fall of HI

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  1. Rise and Fall of HI Ue-Li Pen 彭威礼 Radiative Xfer simulation by Iliev, Mellema & Pen Jeff Peterson, CMU

  2. 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 1016 Mסּ HI. Difficult to observe window, foregrounds. • Mid-z: neutral HI in galaxies, 0.1<z<2. Billions of galaxies, HI mass function evolution poorly known. Intrinsically faint (μJy), requires large collecting area (>105 m2). GMRT/SKA.

  3. Image courtesy of NRAO/AUI and Chung et al., Columbia University

  4. Traditional Radio Telescope Cost Drivers • High Frequency: cryogenic receivers, surface, pointing accuracy • Correlation/bandwidth: N2 cost • General purpose – steerable, reconfigurable • HSHS target: $10/m2, <1.4 GHz, transit • Molonglo actual: $12/m2, steerable cyl • GMRT actual: $100/m2, <1.4 GHz • SKA target: $1000/m2 • VLA actual: $10000/m2

  5. HSHS: Large Area, Low Cost • Surface: low frequency mesh (GMRT) • Structure: passive transit cylinder • Correlations: FFT is N log N instead of N2 • Signal processing: PC’s are $3/Gflop • Astro-ph/0606104

  6. Darwin AUSTRALIA Brisbane Sydney Perth + Molonglo Adelaide Canberra Melbourne Hobart Existing operational cylinders MOLONGLO 1600x12m Cost:$12/m2 (current dollars) OOTY 530x30m Both rotate in one dimension

  7. 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

  8. 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

  9. 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.

  10. Gravitational Lensing: increase flux, decrease density Magnification: increases number of bright galaxies, decreases faint ones.

  11. Four Cylinders each 2 km long, 50m wide • Line feeds at foci used to create 4000 beams N 2 km

  12. CMU Prototype cylinders under construction. Funded by Seljak/Packard

  13. Sept 17 status

  14. Line Feed LNA, $1.81 Filters, $1.99 ea.

  15. 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)

  16. WMAP 3yr: rise of HI τ=0.09+/-0.03, zr=11 Cosmic precombination

  17. White et al 2003: universe fully ionized at z<6

  18. Barkana & Loeb 2001

  19. Reionization • First objects: • 21cm @z=6-15 • 90-200 Mhz • ΔT = 23 mK, • ~μJy- mJy (up to 1016 Mסּ of HI) • Angular scale 5’<Θ<30’, freq res500 khz • Challenging theory z=19-12 simulation, Iliev, Mellema, Pen 2005. 1o FOV

  20. 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

  21. Foreground: Galactic Synchrotron Haslam 408 MHz Much brighter than signal, but no spectral structure

  22. 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).

  23. 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

  24. LOFAR

  25. Mileura Wide-angle Array Photos: Brian Corey and Eric Kratzenberg, MIT Haystack Observatory

  26. 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)

  27. GMRT Search • Operating telescope, 50000m2, 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.

  28. GMRT 150 Mhz image By Ishwara Chandra (NCRA) Image noise 2 mJy Thermal limit 0.5 mJy

  29. Software correlator: $300/node

  30. Power Line Noise Time-lag: Folded 70ms data on short baseline

  31. Comoving distances Low l anomaly: model primary CMB to l~20 CMB reionization ISW: lensing map predictions T-E correlations: can be predicted! EoR Pen 2003

  32. Potential Theoretical Benefits • Precision measurement of power spectrum at 10-8 accuracy (beyond PAST) • Dark energy dynamics: q0, a(t), ISW, dark matter dynamics/clustering (through lensing), gravity waves. • Initial conditions: 2nd order inflation effects, backreaction, curvature, etc. (through hydrogen matter P(k) and 3pcf).

  33. 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.

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