2. The Cosmic Background Imager
Steven T. Myers
National Radio Astronomy Observatory
Socorro, NM

3. 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

4. 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

5. CBI Instrumentation

6. Site – Northern Chilean Andes

7. The uv plane and l space
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

8. The Aperture Plane
In Fourier optics, the uv plane is the aperture plane
An antenna is sensitive to Fourier modes given by the Fourier transform of its primary beam response
Equivalent to the voltage response pattern over the aperture
The interferometer product is a correlation
A visibility for a given baseline is the cross-correlation of the signals from a given pair of antennas
Sensitive to Fourier modes given by the cross-correlation of the aperture voltage responses centered on the uv radius
Width of response in uv plane given by aperture diameter in wavelengths
The power spectrum is given by the uv polar angle average of the visibilty amplitude squared

9. Interferometry of the CMB
An interferometer “visibility” in the sky and Fourier planes:
The primary beam and aperture are related by:

10. Mosaicing in the uv plane

11. Power Spectrum and Likelihood
Statistics of CMB (Gaussian) described by power spectrum:
Construct covariance matrices and perform maximum Likelihood calculation:
Break into bandpowers

12. Seven Pillars of the CMB
(of inflationary adiabatic fluctuations)
Large Scale Anisotropies
Acoustic Peaks/Dips
Damping Tail
Gaussianity
Secondary Anisotropies
Polarization
Gravity Waves
Minimal Inflationary parameter set
Quintessence
Tensor fluc.
Broken Scale Invariance

13. Power Spectrum of the CMB
Courtesy Wayne Hu –

14. Dependence on Geometry
Courtesy Wayne Hu –

15. Dependence on Baryon content
Courtesy Wayne Hu –

16. Dependence on Matter Content
Courtesy Wayne Hu –

17. Courtesy Wayne Hu – http://background.uchicago.edu
Effects of Damping
Courtesy Wayne Hu –

18. Courtesy Wayne Hu – http://background.uchicago.edu
Reionization
Courtesy Wayne Hu –

19. 2ndary SZE Anisotropies
Spectral distortion of CMB
Dominated by massive halos (galaxy clusters)
Low-z clusters: ~ 20’-30’
z=1: ~1’  expected dominant signal in CMB on small angular scales
Amplitude highly sensitive to
pengjie map is 1.19 deg x 1.19 deg; color scale is dT/T=-2y
A. Cooray (astro-ph/ )
P. Zhang, U. Pen, & B. Wang (astro-ph/ )

20. CBI Operations Observing in Chile since Nov 1999
NSF proposal 1994, funding in 1995
Assembled and tested at Caltech in 1998
Shipped to Chile in August 1999
Continued NSF funding in 2002, to end of 2004
Telescope at high site in Andes
16000 ft (~5000 m)
Located on Science Preserve, co-located with ALMA
Now also ATSE (Japan) and APEX (Germany), others
Controlled on-site, oxygenated quarters in containers
Data reduction and archiving at “low” site
San Pedro de Atacama
1 ½ hour driving time to site

21. CBI in Chile

22. CBI 2000 Results Observations Published in series of 5 papers
3 Deep Fields (8h, 14h, 20h)
3 Mosaics (14h, 20h, 02h)
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)

23. 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
Very low fringe rates (susceptible to cross-talk and ground)

24. Calibration and Foreground Removal
Calibration scale ~5%
Jupiter from OVRO 1.5m (Mason et al. 1999)
Agrees with BIMA (Welch) and WMAP
Ground emission removal
Strong on short baselines, depends on orientation
Differencing between lead/trail field pairs (8m in RA=2deg)
Use scanning for polarization observations
Foreground radio sources
Predominant on long baselines
Located in NVSS at 1.4 GHz, VLA 8.4 GHz
Measured at 30 GHz with OVRO 40m
Projected out in power spectrum analysis

25. Power Spectrum Estimation
Method described in Paper IV (Myers et al.)
Large datasets
> 105 visibilities in 6 x 7 field mosaic
~ 103 independent
Gridded “estimators” in uv plane
fast!
Construct covariance matrices for gridded points
Maximum likelihood using BJK method
Output bandpowers
Wiener filtered images constructed from estimators

26. The Gridded Method
Rewrite expression for visibility as convolution in uv plane
Grid up the visibilities using kernel Q
Calculate covariance of gridded estimators

27. Tests with mock data
The CBI pipeline has been extensively tested using mock data
Use real data files for template
Replace visibilties with simulated signal and noise
Run end-to-end through pipeline
Run many trials to build up statistics

28. Wiener filtered images
Covariance matrices can be applied as Wiener filter to gridded estimators
Estimators can be Fourier transformed back into filtered images
Filters CX can be tailored to pick out specific components
e.g. point sources, CMB, SZE
Just need to know the shape of the power spectrum

29. Example – Mock deep field
Noise removed
Raw
CMB
Sources

30. CBI Deep Fields 2000 Deep Field Observations:
3 fields totaling 4 deg^2
~115 nights of observing
Data redundancy  strong tests for systematics

31. CBI 2000 Mosaic Power Spectrum
Mosaic Field Observations
3 fields totaling 40 deg^2
~125 nights of observing
~ 600,000 uv points covariance matrix 5000 x 5000

32. Cosmological Parameters
wk-h: 0.45 < h < 0.9, t > 10 Gyr
HST-h: h = 0.71 ± 0.076
LSS: constraints on s8 and G from 2dF, SDSS, etc.
SN: constraints from Type 1a SNae

33. 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

34. Constraints on SZ “density”
Courtesy J.R. Bond

35. CBI Results

36. CBI and WMAP

37. CBI , WMAP, ACBAR

38. The CMB From NRAO HEMTs

39. Post-WMAP Unification

40. 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

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

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

43. CBI-Pol 2000 Cartwright thesis

44. CBI-Pol Projections

45. 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.