Aspen 2003 Workshop

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The Cosmic Background Imager

• A collaboration between
• Caltech (A.C.S. Readhead PI)
• NRAO
• CITA
• Universidad de Chile
• University of Chicago
• With participants also from
• U.C. Berkeley, U. Alberta, ESO, IAP-Paris,
  NASA-MSFC, Universidad de Concepción
• Funded by
• National Science Foundation, the California
  Institute of Technology, Maxine and Ronald Linde,
  Cecil and Sally Drinkward, Barbara and Stanley
  Rawn Jr., the Kavli Institute, and the Canadian
  Institute for Advanced Research

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The Instrument

• 13 90-cm Cassegrain antennas
• 78 baselines
• 6-meter platform
• Baselines 1m 5.51m
• 10 1 GHz channels 26-36 GHz
• HEMT amplifiers (NRAO)
• Cryogenic 6K, Tsys 20 K
• Single polarization (R or L)
• Polarizers from U. Chicago
• Analog correlators
• 780 complex correlators
• Field-of-view 44 arcmin
• Image noise 4 mJy/bm 900s
• Resolution 4.5 10 arcmin

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Site Northern Chilean Andes
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CBI in Chile
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The CMB and Interferometry

• The sky can be uniquely described by spherical
  harmonics
• CMB power spectra are described by multipole l (
  the angular scale in the spherical harmonic
  transform)
• For small (sub-radian) scales the spherical
  harmonics can be approximated by Fourier modes
• The conjugate variables are (u,v) as in radio
  interferometry
• The uv radius is given by l / 2p
• The projected length of the interferometer
  baseline gives the angular scale
• Multipole l 2p B / l
• An interferometer naturally measures the
  transform of the sky intensity in l space
  convolved with aperture

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CBI Beam and uv coverage

• 78 baselines and 10 frequency channels 780
  instantaneous visibilities
• Frequency channels give radial spread in uv plane
• Pointing platform rotatable to fill in uv
  coverage
• Parallactic angle rotation gives azimuthal spread
• Beam nearly circularly symmetric
• Baselines locked to platform in pointing
  direction
• Baselines always perpendicular to source
  direction
• Delay lines not needed
• Very low fringe rates (susceptible to cross-talk
  and ground)

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CBI 2000 Results

• Observations
• 3 Deep Fields (8h, 14h, 20h)
• 3 Mosaics (14h, 20h, 02h)
• Fields on celestial equator (Dec center 2d30)

• Published in series of 5 papers
• Mason et al. (deep fields)
• Pearson et al. (mosaics)
• Myers et al. (power spectrum method)
• Sievers et al. (cosmological parameters)
• Bond et al. (high-l anomaly and SZ)

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CBI Deep Fields 2000

• Deep Field Observations
• 3 fields totaling 4 deg2
• Fields at d0 a8h, 14h, 20h
• 115 nights of observing
• Data redundancy ? strong tests for systematics

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CBI 2000 Mosaic Power Spectrum

• Mosaic Field Observations
• 3 fields totaling 40 deg2
• Fields at d0 a2h, 14h, 20h
• 125 nights of observing
• 600,000 uv points ?covariance matrix 5000 x
  5000

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SZE Angular Power Spectrum
Bond et al. 2002

• Smooth Particle Hydrodynamics (5123) Wadsley et
  al. 2002
• Moving Mesh Hydrodynamics (5123) Pen 1998

• 143 Mpc ??81.0
• 200 Mpc ??81.0
• 200 Mpc ??80.9
• 400 Mpc ??80.9

Dawson et al. 2002
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Constraints on SZ density

• Combine CBI BIMA (Dawson et al.) 30 GHz with
  ACBAR 150 GHz (Goldstein et al.)
• Non-Gaussian scatter for SZE
• increased sample variance (factor 3))
• Uncertainty in primary spectrum
• due to various parameters, marginalize
• Explained in Goldstein et al. (astro-ph/0212517)
• Use updated BIMA (Carlo Contaldi)

Courtesy Carlo Contaldi (CITA)
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SZE with CBI z lt 0.1 clusters
Udomprasert 2003, PhD thesis, Caltech
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New Calibration from WMAP Jupiter

• Old uncertainty 5
• 2.7 high vs. WMAP Jupiter
• New uncertainty 1.3
• Ultimate goal 0.5

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CBI 20002001 Results
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CBI 20002001, WMAP, ACBAR
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The CMB From NRAO HEMTs
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CBI COBE
weak prior t gt 1010 yr 0.45
lt h lt 0.9 Wm gt 0.1
LSS prior constraint on amplitude of s8
and shape of Geff (Bond et al. Ap.J. 2003)
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CBI Polarization

• CBI instrumentation
• Use quarter-wave devices for linear to circular
  conversion
• Single amplifier per receiver either R or L only
  per element
• 2000 Observations
• One antenna cross-polarized in 2000 (Cartwright
  thesis)
• Only 12 cross-polarized baseline (cf. 66 parallel
  hand)
• Original polarizers had 5-15 leakage
• Deep fields, upper limit 8 mK
• 2002 Upgrade
• Upgrade in 2002 using DASI polarizers
  (switchable)
• Observing with 7R 6L starting Sep 2002
• Raster scans for mosaicing and efficiency
• New TRW InP HEMTs from NRAO

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Pol 2003 DASI WMAP
Courtesy Wayne Hu http//background.uchicago.edu
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Polarization Sensitivity
CBI is most sensitive at the peak of the
polarization power spectrum
The compact configuration
TE
EE
Theoretical sensitivity (1s) of CBI in 450 hours
(90 nights) on each of 3 mosaic fields 5 deg sq
(no differencing), close-packed configuration.
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CBI-Pol 2002-2003 Projections
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Conclusions from CBI Data

• Definitive measurement of diffusive damping
  scale
• Measurements of 3rd 4th Acoustic Peaks
• At Low L ? consistent with other experiments
• At High L (gt2000) ? indications of secondary
  anisotropy?

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Conclusions from CBI Data

• Definitive measurement of diffusive damping
  scale
• Measurements of 3rd 4th Acoustic Peaks
• At Low L ? consistent with other experiments
• At High L (gt2000) ? indications of secondary
  anisotropy?

• Small Scale Power
• 3 sigma above expected intrinsic anisotropy
• Not consistent with likely residual radio source
  populations (more definitive characterization
  needed)
• Suggestive of secondary SZ anisotropy, although
  this would imply sigma8 1
• Other possible foregrounds not ruled out at this
  point

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The CBI Collaboration
Caltech Team Tony Readhead (Principal
Investigator), John Cartwright, Alison Farmer,
Russ Keeney, Brian Mason, Steve Miller, Steve
Padin (Project Scientist), Tim Pearson, Walter
Schaal, Martin Shepherd, Jonathan Sievers, Pat
Udomprasert, John Yamasaki. Operations in Chile
Pablo Altamirano, Ricardo Bustos, Cristobal
Achermann, Tomislav Vucina, Juan Pablo Jacob,
José Cortes, Wilson Araya. Collaborators Dick
Bond (CITA), Leonardo Bronfman (University of
Chile), John Carlstrom (University of Chicago),
Simon Casassus (University of Chile), Carlo
Contaldi (CITA), Nils Halverson (University of
California, Berkeley), Bill Holzapfel (University
of California, Berkeley), Marshall Joy (NASA's
Marshall Space Flight Center), John Kovac
(University of Chicago), Erik Leitch (University
of Chicago), Jorge May (University of Chile),
Steven Myers (National Radio Astronomy
Observatory), Angel Otarola (European Southern
Observatory), Ue-Li Pen (CITA), Dmitry Pogosyan
(University of Alberta), Simon Prunet (Institut
d'Astrophysique de Paris), Clem Pryke (University
of Chicago).
The CBI Project is a collaboration between the
California Institute of Technology, the Canadian
Institute for Theoretical Astrophysics, the
National Radio Astronomy Observatory, the
University of Chicago, and the Universidad de
Chile. The project has been supported by funds
from the National Science Foundation, the
California Institute of Technology, Maxine and
Ronald Linde, Cecil and Sally Drinkward, Barbara
and Stanley Rawn Jr., the Kavli Institute,and the
Canadian Institute for Advanced Research.
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Interferometry of the CMB

• An interferometer visibility in the sky and
  Fourier planes

• The primary beam and aperture are related by

CBI
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Polarization Interferometry
Cross hands sensitive to linear polarization
(Stokes Q and U)
where the baseline parallactic angle is defined
as
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E and B modes

• A useful decomposition of the polarization signal
  is into gradient and curl modes E and B