1UNM – Oct 14, 2003

The Cosmic Background Imager

Steven T. Myers

National Radio Astronomy Observatory

Socorro, NM

2UNM – Oct 14, 2003

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

3UNM – Oct 14, 2003

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

4UNM – Oct 14, 2003

3-Axis mount : rotatable platform

UNM – Oct 14, 2003 5

Other Interferometers: DASI, VSA

• DASI @ South Pole

• VSA @ Tenerife

6UNM – Oct 14, 2003

CBI Instrumentation

7UNM – Oct 14, 2003

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

8UNM – Oct 14, 2003

Site – Northern Chilean Andes

9UNM – Oct 14, 2003

CBI in Chile

10UNM – Oct 14, 2003

A Theoretical Digression

11UNM – Oct 14, 2003

The Cosmic Microwave Background

• Discovered 1965 (Penzias & Wilson)– 2.7 K blackbody– Isotropic– Relic of hot “big bang”– 3 mK dipole (Doppler)

• COBE 1992– Blackbody 2.725 K– Anisotropies 10-5

12UNM – Oct 14, 2003

Thermal History of the Universe

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

13UNM – Oct 14, 2003

CMB Anisotropies

• Primary Anisotropies– Imprinted on surface of “last scattering”– “recombination” of hydrogen z~1100– Primordial (power-law?) spectrum of potential fluctuations

• Collapse of dark matter potential wells inside horizon

• Photons coupled to baryons >> acoustic oscillations!

– Electron scattering density & velocity• Velocity produces quadrupole >> polarization!

– Transfer function maps P(k) >> Cl

• Depends on cosmological parameters >> predictive!

– Gaussian fluctuations + isotropy• Angular power spectrum contains all information

• Secondary Anisotropies– Due to processes after recombination

14UNM – Oct 14, 2003

Acoustic Oscillations

15UNM – Oct 14, 2003

Power Spectrum of the CMB

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

16UNM – Oct 14, 2003

Dependence on Geometry

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

17UNM – Oct 14, 2003

Dependence on Baryon content

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

18UNM – Oct 14, 2003

Effects of Damping

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

19UNM – Oct 14, 2003

Secondary Anisotropies

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

20UNM – Oct 14, 2003

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

Gravitational Secondaries

• Due to CMB photons passing through potential fluctuations (spatial and temporal)

• Includes:– Early ISW (decay, matter-radiation transition at last scattering)– Late ISW (decay, in open or lambda model)– Rees-Sciama (growth, non-linear structures)– Tensors (gravity waves, ‘nuff said)– Lensing (spatial distortions)

21UNM – Oct 14, 2003

Scattering Secondaries

• Due to variations in:– Density

• Linear = Vishniac effect

• Clusters = thermal Sunyaev-Zeldovich effect

– Velocity (Doppler)• Clusters = kinetic SZE

– Ionization fraction• Coherent reionization suppression

• “Patchy” reionization

22UNM – Oct 14, 2003

• 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 8

A. Cooray (astro-ph/0203048)

P. Zhang, U. Pen, & B. Wang (astro-ph/0201375)

2ndary SZE Anisotropies

23UNM – Oct 14, 2003

Seven Pillars of the CMB

•Large Scale Anisotropies

•Acoustic Peaks/Dips

•Damping Tail

•Gaussianity

•Secondary Anisotropies

•Polarization

•Gravity Waves

Minimal Inflationary parameter set

Quintessence

Tensor fluc.

Broken Scale Invariance

(of inflationary adiabatic fluctuations)

24UNM – Oct 14, 2003

Images of the CMB

BOOMERANG

WMAP Satellite

ACBAR

25UNM – Oct 14, 2003

After WMAP…

• Power spectrum– measured to l < 1000– Primary CMB– First 3 peaks

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

26UNM – Oct 14, 2003

…and Planck

• Power spectrum– measured to l < 1000– Primary CMB– First 6 peaks

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

27UNM – Oct 14, 2003

CMB Interferometry

28UNM – Oct 14, 2003

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Interferometers

• Spatial coherence of radiation pattern contains information about source structure– Correlations along wavefronts

• Equivalent to masking parts of a telescope aperture– Sparse arrays = unfilled aperture– Resolution at cost of surface brightness sensitivity

• Correlate pairs of antennas– “visibility” = correlated fraction of total signal

• Fourier transform relationship with sky brightness– Van Cittert – Zernicke theorem

29UNM – Oct 14, 2003

The Fourier Relationship

• An interferometer “visibility” in the sky and Fourier planes:

• The aperture (antenna) size smears out the coherence function response– Like a double-slit experiment with widening slits– Interference plus diffraction pattern– Lose ability to localize wavefront direction = field-of-view– Small apertures = wide field

30UNM – Oct 14, 2003

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 / 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

31UNM – Oct 14, 2003

Interferometry of the CMB

• An interferometer “visibility” in the sky and Fourier planes:

• The primary beam and aperture are related by:

CBI:

CMB peaks smaller

than this !

32UNM – Oct 14, 2003

Mosaicing in the uv plane

33UNM – Oct 14, 2003

Power Spectrum and Likelihood

• Statistics of CMB (Gaussian) described by power spectrum:

Break into bandpowers Construct covariance matrices and perform maximum Likelihood calculation:

34UNM – Oct 14, 2003

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)

35UNM – Oct 14, 2003

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 2002-2003 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

36UNM – Oct 14, 2003

Power Spectrum Estimation

• Method described in Paper IV (Myers et al. 2003)• Large datasets

– > 105 visibilities in 6 x 7 field mosaic– ~ 103 independent

• Gridded “estimators” in uv plane– fast! – Not lossless, but information loss insignificant

• Construct covariance matrices for gridded points• Maximum likelihood using BJK method• Output bandpowers• Wiener filtered images constructed from estimators

37UNM – Oct 14, 2003

The Computational Problem

38UNM – Oct 14, 2003

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

39UNM – Oct 14, 2003

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

40UNM – Oct 14, 2003

Example – Mock deep field

Raw

CMB

Noise removed

Sources

41UNM – Oct 14, 2003

CBI Results

42UNM – Oct 14, 2003

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 (ApJ July 2003)– 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) pending

43UNM – Oct 14, 2003

CBI Deep Fields 2000

Deep Field Observations: •3 fields totaling 4 deg^2•Fields at ~0 =8h, 14h, 20h

•~115 nights of observing•Data redundancy strong tests for systematics

44UNM – Oct 14, 2003

Mosaic Field Observations• 3 fields totaling 40 deg^2• Fields at ~0 =2h, 14h, 20h

• ~125 nights of observing• ~ 600,000 uv points covariance matrix 5000 x 5000

CBI 2000 Mosaic Power Spectrum

45UNM – Oct 14, 2003

CBI 2000 Mosaic Power Spectrum

46UNM – Oct 14, 2003

Cosmological Parameters

wk-h: 0.45 < h < 0.9, t > 10 Gyr

HST-h: h = 0.71 ± 0.076

LSS: constraints on8 and from 2dF, SDSS, etc.

SN: constraints from Type 1a SNae

47UNM – Oct 14, 2003

SZE Angular Power SpectrumSZE Angular Power Spectrum

•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

[Bond et al. 2002]

Dawson et al. 2002

48UNM – Oct 14, 2003

• 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)

Constraints on SZ “density”

Courtesy Carlo Contaldi (CITA)

49UNM – Oct 14, 2003

SZE with CBI: z < 0.1 clusters

50UNM – Oct 14, 2003

New : Calibration from WMAP Jupiter

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

51UNM – Oct 14, 2003

49

Future plans

New: CBI 2000+2001 Results

52UNM – Oct 14, 2003

CBI 2000+2001 Noise Power

53UNM – Oct 14, 2003

CBI 2000+2001 and WMAP

54UNM – Oct 14, 2003

CBI 2000+2001, WMAP, ACBAR

55UNM – Oct 14, 2003

The CMB From NRAO HEMTs

56UNM – Oct 14, 2003

Post-WMAP Unification

57UNM – Oct 14, 2003

weak prior: t > 1010 yr 0.45 < h < 0.9 m > 0.1

LSS prior: constraint on amplitude of 8 andshape of eff (Bond et al. Ap.J. 2003)

CBI + COBECBI + COBE

58UNM – Oct 14, 2003

weak prior: t > 1010 yr 0.45 < h < 0.9 m > 0.1

59UNM – Oct 14, 2003

CBI Current & Future

60UNM – Oct 14, 2003

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 K

• 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

Ka-band Receiver

0

2

4

6

8

10

12

14

16

18

20

26 28 30 32 34 36 38 40

Frequency (GHz)

No

ise

Tem

per

atu

re (

K)

61UNM – Oct 14, 2003

Polarization Sensitivity

CBI is most sensitive at the peak of the polarization power spectrum

Theoretical sensitivity ± of CBI in 450 hours (90 nights) on each of 3 mosaic fields 5 deg sq (no differencing), close-packed configuration.

EETE The compact configuration

62UNM – Oct 14, 2003

Polarization Interferometry

“Cross hands” sensitive to linear polarization (Stokes Q and U):

where the baseline parallactic angle is defined as:

63UNM – Oct 14, 2003

E and B modes

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

64UNM – Oct 14, 2003

CBI-Pol 2000 Cartwright thesis

65UNM – Oct 14, 2003

Pol 2003 – DASI & WMAP

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

66UNM – Oct 14, 2003

CBI-Pol 2002-2004 Projections

67UNM – Oct 14, 2003

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?

68UNM – Oct 14, 2003

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

69UNM – Oct 14, 2003

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.

70UNM – Oct 14, 2003