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The Cosmic Background Imager

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

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The Cosmic Background Imager

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  1. 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

  2. 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

  3. Site – Northern Chilean Andes

  4. CBI in Chile

  5. 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 = 2pB / l • An interferometer naturally measures the transform of the sky intensity in l space convolved with aperture

  6. 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)

  7. 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)

  8. CBI Deep Fields 2000 • Deep Field Observations: • 3 fields totaling 4 deg^2 • Fields at d~0 a=8h, 14h, 20h • ~115 nights of observing • Data redundancy  strong tests for systematics

  9. CBI 2000 Mosaic Power Spectrum • Mosaic Field Observations • 3 fields totaling 40 deg^2 • Fields at d~0 a=2h, 14h, 20h • ~125 nights of observing • ~ 600,000 uv points covariance matrix 5000 x 5000

  10. SZE Angular Power Spectrum [Bond et al. 2002] • Smooth Particle Hydrodynamics (5123) [Wadsley et al. 2002] • Moving Mesh Hydrodynamics (5123) [Pen 1998] • 143 Mpc 8=1.0 • 200 Mpc 8=1.0 • 200 Mpc 8=0.9 • 400 Mpc 8=0.9 Dawson et al. 2002

  11. 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)

  12. SZE with CBI: z < 0.1 clusters Udomprasert 2003, PhD thesis, Caltech

  13. New : Calibration from WMAP Jupiter • Old uncertainty: 5% • 2.7% high vs. WMAP Jupiter • New uncertainty: 1.3% • Ultimate goal: 0.5%

  14. CBI 2000+2001 Results

  15. CBI 2000+2001, WMAP, ACBAR

  16. The CMB From NRAO HEMTs

  17. CBI + COBE weak prior: t > 1010 yr 0.45 < h < 0.9 Wm > 0.1 LSS prior: constraint on amplitude of s8 and shape of Geff (Bond et al. Ap.J. 2003)

  18. weak prior: t > 1010 yr 0.45 < h < 0.9 Wm > 0.1

  19. 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

  20. Pol 2003 – DASI & WMAP Courtesy Wayne Hu – http://background.uchicago.edu

  21. 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.

  22. CBI-Pol 2002-2003 Projections

  23. 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 (>2000)  indications of secondary anisotropy?

  24. 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 (>2000)  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

  25. 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.

  26. CMB peaks smaller than this ! Interferometry of the CMB • An interferometer “visibility” in the sky and Fourier planes: • The primary beam and aperture are related by: CBI:

  27. Polarization Interferometry “Cross hands” sensitive to linear polarization (Stokes Q and U): where the baseline parallactic angle is defined as:

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

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