2. The Cosmic Background Imager – AAS Denver, June 2004 2 Latest Results from the Cosmic Background Imager Steven T. Myers National Radio Astronomy Observatory Socorro, NM

3. The Cosmic Background Imager – AAS Denver, June 2004 3 A Theoretical Digression

4. The Cosmic Background Imager – AAS Denver, June 2004 4 The Cosmic Microwave Background Discovered 1965 ( Penzias & Wilson ) –2.7 K blackbody –Isotropic –Relic of hot “big bang” –Last scattering “surface” z ~ 1000 COBE 1992 –Blackbody 2.725 K –3 mK dipole (Doppler) –Anisotropies 10 -5

5. The Cosmic Background Imager – AAS Denver, June 2004 5 Primary Anisotropies Courtesy Wayne Hu – http://background.uchicago.edu

6. The Cosmic Background Imager – AAS Denver, June 2004 6 Secondary Anisotropies Courtesy Wayne Hu – http://background.uchicago.edu

7. The Cosmic Background Imager – AAS Denver, June 2004 7 CMB Polarization Due to quadrupolar intensity field at scattering Courtesy Hu & White– http://background.uchicago.edu

8. The Cosmic Background Imager – AAS Denver, June 2004 8 Polarization Power Spectra Hu & Dodelson ARAA 2002

9. The Cosmic Background Imager – AAS Denver, June 2004 9 CMB State of the Art: WMAP + “ext” WMAP Satellite

10. The Cosmic Background Imager – AAS Denver, June 2004 10 The Cosmic Background Imager

11. The Cosmic Background Imager – AAS Denver, June 2004 11 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

12. The Cosmic Background Imager – AAS Denver, June 2004 12 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

13. The Cosmic Background Imager – AAS Denver, June 2004 13 Site – Northern Chilean Andes

14. The Cosmic Background Imager – AAS Denver, June 2004 14 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 / 2  The projected length of the interferometer baseline gives the angular scale –Multipole l = 2  B / An interferometer naturally measures the transform of the sky intensity in l space convolved with aperture

15. The Cosmic Background Imager – AAS Denver, June 2004 15 3-Axis mount : rotatable platform

16. The Cosmic Background Imager – AAS Denver, June 2004 16 CBI Beam and uv coverage Over-sampled uv-plane –excellent PSF –allows fast gridded method (Myers et al. 2000)

17. The Cosmic Background Imager – AAS Denver, June 2004 17 New: 2000+2001 Extended Mosaics CBI field-of-view 45’ →  l ~180 –narrow CMB peaks, mosaicing required!

18. The Cosmic Background Imager – AAS Denver, June 2004 18 New: CBI 2000+2001 Results Noise Power Resid. Sources

19. The Cosmic Background Imager – AAS Denver, June 2004 19 CBI 2000+2001, WMAP, ACBAR

20. The Cosmic Background Imager – AAS Denver, June 2004 20 New: Cosmological Parameters Data: –WMAP –CBI + WMAP –CBI + ALL Priors: –flat  tot =1 –45 < H 0 < 90 –t 0 > 10 Gyr Reference: –Readhead et al. ApJ in press (2004) astro-ph/0402359

21. The Cosmic Background Imager – AAS Denver, June 2004 21 New: Running Spectral Index? Data: –WMAP –CBI + WMAP –CBI + ALL + LSS prior Weak Priors: –flat  tot =1 –45 < H 0 < 90 –t 0 > 10 Gyr Combination: –  8 vs.  s

22. The Cosmic Background Imager – AAS Denver, June 2004 22 Dawson et al. 2002 SZE Angular Power Spectrum Smooth Particle Hydrodynamics (512 3 ) [Wadsley et al. 2002] Moving Mesh Hydrodynamics (512 3 ) [Pen 1998] 143 Mpc  8 =1.0 200 Mpc  8 =1.0 200 Mpc  8 =0.9 400 Mpc  8 =0.9 [Bond et al. 2002]

23. The Cosmic Background Imager – AAS Denver, June 2004 23 New: High l excess & ambient SZ? Data: –CBI + BIMA –CBI + BIMA + ACBAR Details: –non-Gaussian correction (F=3) References: –BIMA 30GHz Dawson et al. 2002 –ACBAR Goldstein et al. 2003 Kuo et al. 2004

24. The Cosmic Background Imager – AAS Denver, June 2004 24 SZE with CBI: z < 0.1 clusters Udomprasert 2003, PhD thesis, Caltech

25. The Cosmic Background Imager – AAS Denver, June 2004 25 CBI Polarization

26. The Cosmic Background Imager – AAS Denver, June 2004 26 Polarization Interferometry CBI receivers can observe either R or L circular pol –RR and LL measure CMB intensity (temperature) I –RL and LR measure CMB polarization Q,U

27. The Cosmic Background Imager – AAS Denver, June 2004 27 Polarization E and B modes A useful decomposition of the polarization signal is into gradient and curl modes – E and B: The CBI measures E & B “directly” !

28. The Cosmic Background Imager – AAS Denver, June 2004 28 Polarization Issues Low signal levels –High sensitivity and long integrations needed –Prone to systematics and foreground contamination Instrumental polarization –Well-calibrated system necessary –Straightforward for interferometry (leakage R↔L) Stray radiation –Sky (atmosphere) ~unpolarized (good!) –Ground highly polarized (bad!) –Scan differencing or projection necessary Computationally intensive! –covariances TT, EE, BB, TE, EB, TB plus N and C srcs –6 x 6 mosaics with scan projection C scan

29. The Cosmic Background Imager – AAS Denver, June 2004 29 DASI & WMAP Polarization Courtesy Wayne Hu – http://background.uchicago.edu http://astro.uchicago.edu/dasi/polexpert/

30. The Cosmic Background Imager – AAS Denver, June 2004 30 CBI Current Polarization Data Observing since Sep 2002 in compact configuration –Data processed through May 2004 Four mosaics 02 h, 08 h, 14 h, 20 h –02h, 08h, 14h 6 x 6 fields, 45’ centers –20h deep strip 6 fields Scan subtraction/projection –observe scan of 6 fields, 3m apart = 45’ –lose on 1/6 data to differencing (cf. ½ previously) Point source projection –list of NVSS sources (extrapolation to 30 GHz unknown) –need 30 GHz GBT measurements to identify brightest srcs

31. The Cosmic Background Imager – AAS Denver, June 2004 31 CBI Polarization Projections

32. The Cosmic Background Imager – AAS Denver, June 2004 32 CBI Polarization Data Processing Massive data processing exercise –4 mosaics, 300 nights observing –more than 10 6 visibilities total! –scan projection over 3.5° requires fine gridding more than 10 4 gridded estimators Parallel computing critical –both gridding and likelihood now parallelized using MPI using 256 node/ 512 proc McKenzie cluster at CITA 2.4 GHz Intel Xeons, gigabit ethernet, 1.2 Tflops! current limitation 1 GB memory per node –code development ongoing currently 1 day per full run needed

33. The Cosmic Background Imager – AAS Denver, June 2004 33 CBI Current Polarization Data Currently data to May 2004 processed –Preliminary data analysis (still more tests pending) if you sign the non-disclosure agreement…

34. The Cosmic Background Imager – AAS Denver, June 2004 34 Conclusions CMB interferometry competitive –straightforward analysis {RR,RL} → {TT,EE,BB,TE} –polarization systematics minimized –currently only measurements of EE (WMAP pending) –but, hard to scale up due to correlator complexity CMB results –large l TT excess still significant next gen small-scale experiments (SZA) will nail this! –possible running index n s ( l ) marginal significance (probably overstated) –polarization observations successful results very preliminary! still more tests…

35. The Cosmic Background Imager – AAS Denver, June 2004 35 The CMB From NRAO HEMTs OVRO/BIMA

36. The Cosmic Background Imager – AAS Denver, June 2004 36 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.