Dark Energy Radio HI Surveys

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Dark Energy Radio HI Surveys

• Ue-Li Pen
• ???

SKA artist conception
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Dark Energy Measurements

• Geometric Baryon Acoustic Oscillations (CMB, HI,
  optical), lensing geometry, SNe luminosity
  distance.
• Dynamical gravity dark matter (lensing
  tomography, cluster mass evolution)
• Dynamical energy measure spatial perturbations
  in the dark energy field (ISW)

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Radio vs Optical

• Complementary approaches.
• Historically, radio was an early window to high-z
  universe, but required optical follow-up for
  astrometry and redshifts.
• Today, radio astrometry is unmatched. High-z
  searches dominated by optical, but redshifts are
  very challenging in range of interest (z1-2).
• Revolution possible with billion HI redshifts

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Image courtesy of NRAO/AUI and Chung et al.,
Columbia University
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Existing operational cylinders
MOLONGLO 1600x12m Cost12/m2 (current dollars)
OOTY (India) 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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Indian Giant Meterwave Radio Telescope
30 dishes _at_45m ea. Operates at lt1.5 GHz
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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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Hubble Sphere Hydrogen Survey
HSHS Large Area, Low Cost

• Jeff Peterson, Uros Seljak, CEA, LAL, South
  Africa, Australia
• Map 109 galaxy 21cm redshifts to zlt1.5 for Baryon
  acoustic oscillations, weak lensing
• Dark energy parameters
• Low cost, fast time scale.
• Astro-ph/0606104

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• passive transit cylinder
• Correlations FFT is N log N instead of N2
• Astro-ph/0606104
• Collaborators CEA, ETH, SA

Jeff Peterson Jan 2007
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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
Zwann et al
Magnification increases number of bright
galaxies, decreases faint ones.
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Magnification Lensing

• Bright-faintlensing
• Brightfaintintrinsic clustering
• Almost orthogonal measurements if distances are
  known
• May overcome all known systematic limitations to
  shear lensing (PSF, intrinsic alignment, z-dist),
  similar sensitivity.
• Well suited to HI radio surveys and SKA.

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Zhang Pen 2005
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Abdalla Rawlings, 2004
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Dark Energy Accuracy

• From SKA (or similar 109 redshift survey) BAO
• Geometric Lensing (Hu Jain 2004)
• Dynamical lensing (Hu 2003)

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Summary

• Radio and optical have played complementary
  roles, and the future may be for 21cm-radio as
  massive redshift machines to map Hubble Volume.
• In cm-m wavelength, enormous growth potential in
  technology and collecting area
• Billion redshift Hubble Volume survey will be a
  key in dark energy measurement geometric and
  dynamical (BAO, lens, ISW), and targeted by SKA
  and HSHS
• Construction of a billion redshift survey radio
  telescope may be very economical (e.g. HSHS).