Rise and Fall of HI

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Rise and Fall of HI

• Ue-Li Pen ???

Radiative Xfer simulation by Iliev, Mellema Pen
Jeff Peterson, CMU
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Search for Cosmic Hydrogen

• About half of horizon volume filled with HI,
  dominated by zgt6
• hi-z lots out there, structures with up to 1016
  M? HI. Difficult to observe window, foregrounds.
• Mid-z neutral HI in galaxies, 0.1ltzlt2. Billions
  of galaxies, HI mass function evolution poorly
  known. Intrinsically faint (µJy), requires large
  collecting area (gt105 m2). GMRT/SKA.

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Image courtesy of NRAO/AUI and Chung et al.,
Columbia University
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Traditional Radio Telescope Cost Drivers

• High Frequency cryogenic receivers, surface,
  pointing accuracy
• Correlation/bandwidth N2 cost
• General purpose steerable, reconfigurable
• HSHS target 10/m2, lt1.4 GHz, transit
• Molonglo actual 12/m2, steerable cyl
• GMRT actual 100/m2, lt1.4 GHz
• SKA target 1000/m2
• VLA actual 10000/m2

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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 PCs are 3/Gflop
• Astro-ph/0606104

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Existing operational cylinders
MOLONGLO 1600x12m Cost12/m2 (current dollars)
OOTY 530x30m Both rotate in one dimension
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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
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Local HI Luminosity Function
Zwann et al
at z1.5 this is 30 microjansky We detect all
these across 1/2 of sky in 6 months
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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.

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Gravitational Lensing increase flux, decrease
density
Magnification increases number of bright
galaxies, decreases faint ones.
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Four Cylinders each 2 km long, 50m wide

• Line feeds at foci used to create 4000 beams

N
2 km
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CMU Prototype cylinders under construction.
Funded by Seljak/Packard
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Sept 17 status
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Line Feed
LNA, 1.81
Filters, 1.99 ea.
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Additional Science

• Find and monitor 1000s of new pulsars--strongly
  constrain the gravity wave background
• Map galactic magnetic fields
• Study Early Ionization at z gt 13

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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

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HI Evolution

• Major cost uncertainty is luminosity function
  evolution.
• Popular models differ by factor of several
• Effort under way to measure z1.4 mass function
  using DEEP cross correlation (T. Chang, M. Davis,
  U. Seljak)

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WMAP 3yr rise of HI
t0.09/-0.03, zr11
Cosmic precombination
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White et al 2003 universe fully ionized at zlt6
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Barkana Loeb 2001
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Reionization

• First objects
• 21cm _at_ z6-15
• 90-200 Mhz
• ?T 23 mK,
• µJy- mJy (up to 1016 M? of HI)
• Angular scale 5ltTlt30, freq res 500 khz
• Challenging theory

z19-12 simulation, Iliev, Mellema, Pen 2005. 1o
FOV
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Cosmic Reioniation
Largest radiative transfer cosmological
reionization simulations 1 degree FOV. Detection
in 21cm hyperfine transition with radio
telescopes. Structure on large scales
(gt20). Iliev, Mellema, Pen 2006
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Foreground Galactic Synchrotron
Haslam 408 MHz
Much brighter than signal, but no spectral
structure
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Detectability

• Luminosity proportional to object volume bigger
  structures easier to find
• Noise dominated by galaxy T300(?/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).

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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

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LOFAR
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Mileura Wide-angle Array
Photos Brian Corey and Eric Kratzenberg, MIT
Haystack Observatory
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Indian Giant Meterwave Radio Telescope
30 dishes _at_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)
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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.

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GMRT 150 Mhz image By Ishwara Chandra
(NCRA) Image noise 2 mJy Thermal limit 0.5 mJy
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Software correlator 300/node
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Power Line Noise
Time-lag Folded 70ms data on short baseline
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Comoving distances
Low l anomaly model primary CMB to l20
CMB
reionization
ISW lensing map predictions
T-E correlations can be predicted!
EoR
Pen 2003
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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).

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Outlook

• Existing constraints optical depth from WMAP,
  SDSS QSOs.
• Theoretical progress direct simulations indicate
  power on larger scales (gt20), 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.