2. 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

3. The Instrument 13 90-cm Cassegrain antennas 6-meter platform
78 baselines
6-meter platform
Baselines 1m – 5.51m
10 1 GHz channels 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

4. Site – Northern Chilean Andes

5. CBI in Chile

6. 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

7. 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)

8. CBI 2000 Results Observations Published in series of 5 papers
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)

9. 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

10. 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

11. 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
Review SZ effect – expected crossover
Use of simulations to predict power
Description of simulations
Parameters of simulations
Scaling of power with parameters confirms s8to the 7
Power for s8=1 and s8=0.9

12. 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/ )
Use updated BIMA (Carlo Contaldi)
Courtesy Carlo Contaldi (CITA)

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

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

15. CBI Results

16. CBI , WMAP, ACBAR

17. The CMB From NRAO HEMTs

18. 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)

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

20. CBI Polarization CBI instrumentation 2000 Observations 2002 Upgrade
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

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

22. 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.

23. CBI-Pol Projections

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?

25. 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

26. 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.

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

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

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