Rise and Fall of HI
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Transcript of Rise and Fall of HI
Rise and Fall of HI
Ue-Li Pen 彭威礼
Jeff Peterson, CMU
Radiative Xfer simulation by Iliev, Mellema & Pen
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 Mּס 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.
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: 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
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
Existing operational cylinders
MOLONGLO1600x12mCost:$12/m2
(current dollars)
OOTY530x30mBoth rotate in one dimension
Molonglo
AUSTRALIABrisbane
Darwin
PerthCanberra
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 ftTelescope ca. 1960
Local HI Luminosity Function
Zwann et al
at z=1.5 this is 30 microjanskyWe 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
Sept 17 status
Line Feed
LNA, $1.81
Filters,$1.99 ea.
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, zr=11
WMAP 3yr: rise of HI
Cosmic precombination
White et al 2003: universe fully ionized at z<6
Barkana & Loeb 2001
Reionization
• First objects: • 21cm @ z=6-15• 90-200 Mhz• ΔT = 23 mK, • ~μJy- mJy (up to 1016
Mּס of HI)• Angular scale 5’<Θ<3
0’, freq res 500 khz• Challenging theory
z=19-12 simulation, Iliev, Mellema, Pen 2005. 1o 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
LOFAR
Mileura Wide-angle
Array
Photos: Brian Corey and Eric Kratzenberg, MIT Haystack Observatory
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, 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.
GMRT 150 Mhz image
By Ishwara Chandra (NCRA)
Image noise 2 mJy
Thermal limit 0.5 mJy
Software correlator: $300/node
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: 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).
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.