New Results from the Cosmic Background Imager

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New Results from the Cosmic Background Imager
Steven T. Myers
National Radio Astronomy Observatory Socorro, NM
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The Cosmic Background Imager
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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

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3-Axis mount rotatable platform
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CBI Instrumentation
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CBI Operations

• Observing in Chile since Nov 1999
• NSF proposal 1994, funding in 1995 (idea back to
  80s)
• Assembled and tested at Caltech in 1998
• Shipped to Chile in August 1999
• Continued NSF funding in 2002, to end of 2004
• Exploring funding prospects to operate until 2006
• 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)
• Future home of ACT, others?
• Controlled on-site, oxygenated quarters in
  containers
• Data reduction and archiving at low site
• San Pedro de Atacama (1 ½ hour to site)

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Site Northern Chilean Andes
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CBI in Chile
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The CBI Adventure

• sunset

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The CBI Adventure

• Steve Padin wearing the cannular oxygen system

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The CBI Adventure

• Two winters a year! Some 4 wheelin action

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The CBI Adventure

• Two winters a year! The roads fill with snow.

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The CBI Adventure

• Volcan Lascar (30 km away) erupts in 2001

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CMB Interferometers DASI, VSA

• DASI _at_ South Pole

• VSA _at_ Tenerife

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A Theoretical Digression
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Primary Anisotropies
Courtesy Wayne Hu http//background.uchicago.edu
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Secondary Anisotropies
Courtesy Wayne Hu http//background.uchicago.edu
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Gravitational Secondaries

• Due to 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)

Courtesy Wayne Hu http//background.uchicago.edu
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Scattering Secondaries

• Variations in
• Density
• Linear Vishniac effect
• Clusters thermal SZE
• Velocity (Doppler)
• Clusters kinetic SZE
• Ionization fraction
• Coherent reionization suppression
• Patchy reionization

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WMAP Power Spectrum
Courtesy WMAP http//map.gsfc.nasa.gov
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CMB Polarization

• Due to quadrupolar intensity field at scattering
• E B modes
• E (gradient) from scalar density fluctuations
  predominant!
• B (curl) from gravity wave tensor modes, or
  secondaries
• Detected by DASI and WMAP
• EE and TE seen so far, BB null
• Next generation experiments needed for B modes
• WMAP not (likely) sensitive enough
• Science driver for Beyond Einstein mission
• Lensing at sub-degree scales likely to detect
• Tensor modes hard unless T/S0.1 (high!)
• Planck projections

Hu Dodelson ARAA 2002
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CMB Interferometry
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CMB Interferometers

• CMB issues
• Extremely low surface brightness fluctuations lt
  50 mK
• Polarization less than 10 ? signal lt 5 mK
• Large monopole signal 3K, dipole 3 mK
• No compact features, approximately Gaussian
  random field
• Foregrounds both galactic extragalactic
• Traditional direct imaging
• Differential horns or focal plane arrays
• Interferometry
• Inherent differencing (fringe pattern), filtered
  images
• Works in spatial Fourier domain
• Element-based errors vs. baseline-based signals
• Limited by need to correlate pairs of elements
• Sensitivity requires compact arrays

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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

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Traditional Inteferometer The VLA

• The Very Large Array (VLA)
• 27 elements, 25m antennas, 74 MHz 50 GHz (in
  bands)
• located 3 hrs away! 1 hr west of Socorro on US 60

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Polarization of radiation

• Stokes parameters
• intensity I
• fractional polarization (p I)2 Q2 U2
  V2
• linear polarization Q,U (m I)2 Q2 U2
• circular polarization V (v I)2 V2
• Coordinate system dependence
• I independent
• V depends on choice of handedness
• V gt 0 for RCP
• Q,U depend on choice of North (plus handedness)
• Q points North, U 45 toward East
• EVPA F ½ tan-1 (U/Q) (North through East)

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Polarization Stokes parameters

• CBI receivers can observe either RCP or LCP
• cross-correlate RR, RL, LR, or LL from antenna
  pair
• Mapping of correlations (RR,LL,RL,LR) to Stokes
  parameters (I,Q,U,V)
• Intensity I plus linear polarization Q,U
  important
• CMB not circularly polarized, ignore V (RR LL
  I)
• parallel hands RR, LL measure intensity I
• cross-hands RL, LR measure polarization Q, U
• R-L phase gives Q, U electric vector position
  angle

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Aside LP vs. CP basis

• Circularly polarized feeds (e.g. CBI, DASI)
• Linearly polarized feeds (e.g. CAPMAP)

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The Fourier Relationship

• A parallel hand visibility in sky and Fourier
  planes
• direction xk and uk Bk/lk for baseline Bk
• other correlation LL measures same I
• The aperture (antenna) size restricts response
• convolution in uv plane loss of Fourier
  resolution
• multiplication on sky field-of-view
• loss of ability to localize wavefront direction
• Small apertures wide field higher Fourier
  resolution

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uv-plane support

• Visibilities have support in uv plane over
  aperture cross-correlation
• On short baselines, B lt v2 D
  a visibility can correlate with both another
  visibility and its conjugate
• For these cases, real and imaginary covariances
  not independent

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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

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CBI Beam and uv coverage

• 78 baselines and 10 frequency channels 780
  instantaneous visibilities
• Frequency channels give radial spread in uv plane
• 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)
• Pointing platform rotatable to fill in uv
  coverage
• Parallactic angle rotation gives azimuthal spread
• Beam nearly circularly symmetric
• CBI uv plane is well-sampled
• few gaps
• inner hole (1.1D), outer limit dominates PSF

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Field of View and Resolution

• An interferometer visibility in the sky and
  Fourier planes

• The primary beam and aperture are related by

CBI
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Mosaicing in the uv plane
offset add
phase gradients
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Polarization Interferometry

• Cross-hand correlations
• where kernel P is the aperture cross-correlation
  function
• and the baseline parallactic angle

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E and B modes

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

interferometer directly measures E B!
E B response smeared by phase variation over
aperture A
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Power Spectrum of CMB

• Statistics of CMB field
• Gaussian random field Fourier modes independent
• described by angular power spectrum
• 6 polarization covariances TT,TE,TB,EE,EB,BB

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Power Spectrum and Likelihood

• Break Cl into bandpowers qB
• Covariance matrix C sum of individual covariance
  terms
• maximize Likelihood for complex visibilities V

fiducial power spectrum shape (e.g. 2p/l2)
c1 if l in band B else c0
residual (statistical) foreground
known foregrounds (e.g point sources)
scan (ground) signal
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Power Spectrum Estimation

• Method described in CBI Paper 4
• Myers et al. 2003, ApJ, 591, 575
  (astro-ph/0205385)
• The problem - large datasets
• gt 105 visibilities in 6 x 7 field mosaic
• 104 distinct per mosaic pointing!
• But only 103 independent Fourier plane patches
• More problems
• Mosaic data must be processed together
• Data also from 4 independent mosaics!
• Polarization data x3 and covariances x6!
• ML will be O(N3), need to reduce N!
• Solution grid data into smaller number of
  estimators
• gridding convolution kernel matched to A (matched
  filter)

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Gridded estimators and covariances
gridded Fourier plane (l,m)

• Write with operators
• visibilities
• covariance
• convolve with kernel
• covariance
• equivalent to linear mosaic
• matched filter Q

v P t e
C(l,m,l,m)Cldll dmm
lt v v gt P lt t t gt P E E lt e e gt
(diagonal noise)
D Q v R t R Q P
lt D D gt Q lt v v gt Q
R lt t t gt R N
N QEQ
mosaicing phase factor
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Gridded uv-plane estimators

• Method practical efficient
• Reduced to 103 to 104 grid cells
• Not lossless, but information loss insignificant
• Fast! (work spread between gridding covariance)
• Construct covariance matrices for gridded points
• Complicates covariance calculation
• Summary of Method
• time series of calibrated visibilities V
• grid onto D, accumulate R and N (scatter)
• assemble covariances (gather)
• pass to Likelihood (BJK) or Imager
• parallelizable! (gridding easy, ML harder)

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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

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Detail leakage

• Primary on-axis effect is leakage of one
  polarization into the measurement of the other
  (e.g. R ? L)
• but, direction dependence due to polarization
  beam!
• Customary to factor out on-axis leakage into D
  and put direction dependence in beam
• example expand RL basis with on-axis leakage
• similarly for XY basis

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Detail leakage

• In full glory

true signal
2nd order DP into I
2nd order D2I into I
1st order DI into P
3rd order D2P into P
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Detail leakage (upshot)

• measure on bright polarized source (or using
  grid, e.g. DASI)
• to first order
• TT unaffected
• TT leaks into TE TB
• TE TB leak into EE, BB, EB
• include in correlation analysis
• just complicates covariance matrix calculation

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Detail polarized beam (e.g. VLA)

• AIPS Memo 86 Widefield Polarization Correction
  of VLA Snapshot Images at 1.4 GHz W. Cotton
  (1994)
• upshot build into analysis procedure

Circular Polarization
Linear Polarization
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CBI Results
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CBI at the l frontier

• CBI observes angular scales 4'-2
• corresponds to Mpc scales today

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New Calibration from WMAP Jupiter

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

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Calibration and Foreground Removal

• Ground emission removal
• Strong on short baselines, depends on orientation
• Differencing between lead/trail field pairs (8m
  in RA2deg)
• Use scanning for 2002-2003 polarization
  observations

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Foregrounds Sources

• 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
• new 30 GHz GBT receiver

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Foregrounds Sources

• 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
• new 30 GHz GBT receiver
• Projected out in power spectrum analysis
• masking out much of sky need GBT measurements
  to reduce the number of sources projected

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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

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CBI Deep Fields 2000

• Deep Field Observations
• data redundancy ? strong tests for systematics
• 3 fields totaling 4 deg2
• 115 nights of observing

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CBI 2000 Mosaic Power Spectrum

• Mosaic Field Observations
• 3 differenced field pairs totaling 40 deg2
• 125 nights of observing
• 600,000 uv points ?covariance matrix 5000 x
  5000

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New CBI 20002001 Results!

• Observations
• 3 Mosaics (2h, 14h, 20h) extended N-S
• includes 14h and 20h deep fields
• 8h Deep Field
• Analysis
• new calibration vs. WMAP Jupiter
• joint deep/mosaic analysis
• consistent with high-l excess from 2000
• updated parameter constraints
• ApJ (in press)
• Readhead et al. 2004 (astro-ph/0402359)

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New Extended Mosaics

• Combined mosaics deep fields

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New CBI 20002001 Results
Noise Power
Resid. Sources
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New Window Functions

• Extended mosaics allow better l resolution

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CBI 20002001, WMAP, ACBAR
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New Cosmological Parameters

• Data
• WMAP
• CBI WMAP
• CBI ALL
• Priors
• flat Wtot1
• 45 lt H0 lt 90
• t0 gt 10 Gyr

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New Running Spectral Index?

• Data
• WMAP
• CBI WMAP
• CBI ALL LSS prior
• Weak Priors
• flat Wtot1
• 45 lt H0 lt 90
• t0 gt 10 Gyr

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New High l excess ambient SZ?

• Data
• CBI BIMA
• CBI BIMA ACBAR
• Details
• non-Gaussian correction (F3)
• References
• BIMA 30GHz
• Dawson et al. 2002
• ACBAR
• Goldstein et al. 2003
• Kuo et al. 2004

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SZE Angular Power Spectrum
Bond et al. 2002

• Smooth Particle Hydrodynamics (5123) Wadsley et
  al. 2002
• Moving Mesh Hydrodynamics (5123) Pen 1998

• 143 Mpc ??81.0
• 200 Mpc ??81.0
• 200 Mpc ??80.9
• 400 Mpc ??80.9

Dawson et al. 2002
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Constraints on SZ density

• CBI 30 GHz plus
• BIMA 30 GHz (Dawson et al.)
• ACBAR 150 GHz (Goldstein et al.)
• Consistent with LSS determinations
• e.g. clusters, weak lensing

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CBI Polarization
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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 baselines (cf. 66
  parallel hand)
• Original polarizers had 5-15 leakage
• Deep fields, upper limit 8 mK
• 2002 Upgrade
• Upgrade in 2002 using DASI polarizers (J. Kovac)
• Observing with 7R 6L starting Sep 2002
• Raster scans for mosaicing and efficiency
• New TRW InP HEMTs from NRAO

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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.
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CBI-Pol 2000 Cartwright thesis
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Pol 2003 DASI WMAP
Courtesy Wayne Hu http//background.uchicago.edu
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CBI Current Polarization Data

• Observing since Sep 2002
• compact configuration, maximum sensitivity
• Calibration on TauA (Crab) Jupiter
• use TauA to calibrate R-L phase
• Four mosaics 02h, 08h, 14h, 20h
• 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 know brightest

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CBI Polarization Projections
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CBI Polarization Data Processing

• Massive data processing exercise
• 4 mosaics, 300 nights observing
• more than 106 visibilities total!
• scan projection over 3.5 requires fine gridding
• more than 104 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 8 hours per full run needed (for 32
  nodes)

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CBI Current Polarization Data

• Currently data to May 2004 processed
• data analysis underway (still more tests pending)
• results soon

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SZE
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The Sunyaev-Zeldovich Effect

• Inverse Compton upscattering of CMB photons by
  keV electrons in IGM of massive galaxy clusters
• decrement in DT below CMB thermal peak (increment
  above)
• at microwave frequencies, ignoring relativistic
  (in Te) corrections
• y is the Compton y parameter
• power-law density profile
• exponential fall-off with baseline!

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SZE with CBI z lt 0.1 clusters
P. Udomprasert thesis (Caltech)
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CBI SZE visibility function

• Xray ?-3 (b 2/3)
• SZE ?-1 ? -exp(-v)/v
• dominated by shortest baselines

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A85
(left) Raw CBI Image (center) CLEAN source-sub
CBI Image (right) CBI w/ROSAT

• A85 cluster with central cooling flow, some
  signs of merger activity, subcluster to south

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A478
(left) Raw CBI Image (center) CLEAN source-sub
CBI Image (right) CBI w/ROSAT

• A478 relaxed cooling flow cluster, X-ray
  cavities from AGN

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A754
(left) Raw CBI Image (center) CLEAN source-sub
CBI Image (right) CBI w/ROSAT

• A754 prototypical violent merger,
  significantly disturbed

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A2597
(left) Raw CBI Image (center) CLEAN source-sub
CBI Image (right) CBI w/ROSAT

• A2597 regular cD cluster with cooling flow, AGN
  in center (see raw image) with X-ray shadows in
  X-ray

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Results (Udomprasert et al. 2004)

• unweighted H0 67 3018 13 6 km/s/Mpc
• weighted H0 75 2316 15 7 km/s/Mpc
• uncertainties dominated by CMB confusion
• based on older X-ray data

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Gastrophysics?

• mergers A85, A399/401, A754
• A401 A754 somewhat low, A399 very low (but
  uncertain)
• cooling cores A85, A478, A2597
• A478 high, A2597 very high (but uncertain)

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Summary
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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 ns(l)
• marginal significance so far
• EE detected, polarization peaks resolved
• results very preliminary! still more tests
• SZE imaged in nearby clusters
• probes cluster gastrophysics cosmology
• uncertainties dominated by primary CMB on these
  scales!

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The CMB From NRAO HEMTs
OVRO/BIMA
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The Next Generation Experiment

• Q/U Imaging ExperimenT (QUIET) Array
• Development Schedule

Functional 100 GHz Q Element Prototype 10/03
500 ?K?s/Q 100 Element Array 2005 50 ?K?s/Q
1000 Element Q/UArrays 2006 10 ?K?s/Q
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The Next Generation Tech

• Large format focal-plane arrays w/coherent
  detectors

T. Gaier (JPL)
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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.
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