# Presentation: 508934

## Future Ground-based CMB & SZ Interferometry (and some developments for mm spectroscopy)‏

- Sarah Church
- Stanford University/Kavli Institute for Particle Astrophysics and Cosmology
- on behalf of the MAS/CHIP/SZI working groups
- Nov 22nd 2008

## Enabling Technology: JPL development of MMIC modules based on low-noise InP amplifiers

- 1 in

- 1.0 in

**Correlation radiometer for **
**the QUIET experiment (PI Winstein, U. Chicago)****‏**

**Heterodyne module suitable for **
**spectroscopy, interferometer **

## Scalable W-band MMIC Array

- Drawing by J. Lau (Stanford)‏

## Goal is scalability and versatility

- Assume FPGA-based correlator/spectrometer technology
- Moore's Law still working in our favor. Don't build until the last minute!
- Heard this a lot at this workshop

- Potential applications
- CMB interferometer
- Arrays on interferometers to increase mapping speed (SZ)‏
- Spectrometers for Large Aperture Telescopes

## CMB Polarization Science

- Reionization bump

- X300 fainter!

**B modes (parity) from primordial gravitational waves**

*Hu, Hedman, Zaldarriga, 2002*

- Gravitationally lensed E-modes (dark energy, massive neutrinos)‏

- E-mode polarization (no parity) from density fluctuations

- Inflation???

**Also very important tests of  inflation from measurements of the gaussianity (or otherwise of the fluctuations)****‏**

- WMAP polarization map

## The QUaD experiment (Church US PI, Gear UK PI)‏

- The QUaD experiment (Church US PI, Gear UK PI)‏

- Scan backwards and forwards in azimuth

- 90, 150 GHz

- Stokes U map

- Pryke et al., arXiv:0805.1944

## The QUaD people

**Stanford University/KIPAC**
- -- Sarah Church, Melanie Bowden, Keith Thompson, Ed Wu
**University of Chicago/KICP**
- -- Clem Pryke, John Carlstrom, Tom Culverhouse, Erik Leitch, Robert Friedman, Robert Schwarz
**Caltech**
- -- Andrew Lange, John Kovac, Angiola Orlando
**JPL/IPAC **
- -- Jamie Bock, Ben Rusholme, Mike Zemcov
**NASA Goddard**
- -- Jamie Hinderks

**Cardiff University **
- -- Walter Gear, Peter Ade, Sujarta Gupta, Abigail Turner
**University of Edinburgh**
- -- Andy Taylor
**University of Cambridge**
- -- Michael Brown
**Laboratoire APC/CNRS**
- -- Ken Ganga
**Universidade Técnica de Lisboa**
- -- Patricia Castro
**Manchester University**
- -- Lucio Piccirillo, Simon Melhuish
**Maynooth College, Ireland**
- -- Anthony Murphy, Creidhe O'Sullivan, Gary Cahill** **

- Ade et al., arXiv:0705.2359
- Hinderks et al., arXiv:0805.1990
- Pryke et al., arXiv:0805.1944
- Wu et al., arXiv:0811.0618

## Lessons from QUaD -- systematics

- Gain mismatches between two detectors differenced to measure Q or U
- Pointing mismatches between two detectors that are differenced to measure Q or U
- Cross-polarization at the few percent level
- Long time constants that are not pure exponentials
- Ground pickup in sidelobes
- Beam width uncertainty limits high-*l* measurements
**Every single one of these effects required many months of modeling to mitigate and usually required “unfixable” data to be discarded**
**We need to pay close attention to the design**

## Measuring E and B with QUaD detectors

- Trench removes 1/f noise from atmosphere and detectors and ground pickup (telescope sidelobes)‏

**U**

**Q**

- Recover *E* and *B* modes from Fourier plane

*u*

*v*

**

- (*u**0 **,v*0)‏

## QUaD -- Contamination visible in Fourier Plane

- 1/f noise from atmosphere and detectors
- Ground pickup (telescope sidelobes)‏

- Signal

- Jack knife

## Why Interferometers are especially well suited to CMB measurements

- L1 * L2   T + *i*V
- R1 * R2  T - *i*V
- L1 * R2  Q + *i*U
- R1 * L2  Q - *i*U

- DASI interferometer
- http://astro.uchicago.edu/cara/vtour/pole/darksector/cmbr/sunset.jpg

- All 4 Stokes parameters are  *simultaneously measured in Fourier space*
*Time-dependent drifts are strongly rejected and don't generate false low-l data (key for B-mode measurements)**‏*
-   Can use corrugated feedhorns with very low sidelobes
-   Low resolution spectroscopy (4-5 GHz sub bands) can help to distinguish foregrounds

## Previous CMB interferometers

- DASI
- University of Chicago
- First detection of polarization in the microwave background radiation

- CBI, Caltech
- High-l measurements of CMB
- CMB polarization measurements superceded only by QUaD

- Radio interferometers played a key role in measurements of the CMB

- Kovac et al. 2005

- Pearson et al. 2005

## Projected sensitivity to Stokes parameters of InP amplifiers on ground-based expts

- 25% band assumed
- Bolo numbers from Kovac (Caltech)‏
- 10K telescope temperature assumed
- Bolometers assume to measure only Q or U; amplifiers are measuring both

## Large-format interferometer enabled by scalable technology

- Drawing by J. Lau (Stanford)‏

## Strawman CMB Interferometer

- 100 dual-polarization pixels with corrugated feed horns in a close-packed array – basic unit
- Shortest baseline 7 (small horns!)‏. Entire array is only a few tens of cm across
- Cross correlate all possible baselines
- RR, LL, RL, LR
- 25% bandwidth
- Get more sensitivity by building more 100-element arrays
- Phase I – 1-2 arrays
- Phase II – 6+ arrays
- No cross-correlation between arrays
*Extremely* versatile – can grow as correlator capabilities improve
- Can scale horn size if smaller angular scales required

## Sensitivity example (no foregrounds, 2 years) 

## SZ Interferometry -- Science From Studies of the SZ Effect in Individual Clusters

**Large Relaxed Systems**
- Combine SZ and X-ray measurements to determine angular diameter distances
- Measure gas masses and baryon fractions by combining with X-ray measurements
- Non-relaxed systems
- Probe the gas distribution to understand the gas physics
- Calibrate SZ-flux to mass scaling relationships
- Important follow-up for cluster surveys
- Measure cluster gas temperatures through the relativistic correction to the SZ effect??
- Measure gas velocities from the kinematic SZ effect??

## X-ray map of cluster RXJ1347-1145Allen, Schmidt, Fabian( 2005)‏

- Ideally an SZ Interferometer would match X-ray resolution
- A Southern Hemisphere SZ Interferometer would be a great follow-up instrument for SPT, ACT and would enable important single cluster science.

## Constraining power of joint SZ/X-ray of 1000 clusters

- Allen et al., 2008 arXiv:0706.0033

- Rapetti et al., 2006 arXiv:0608.0009

- X-ray fgas

- SZ and X-ray DA

## Interferometers for SZ

- Advantages
**Angular resolution and field of view can be tailored by size and position of dishes.**
- Atmosphere is in near field of array and is strongly filtered
- Ground signal is strongly attenuated, especially by a tracking array
- Heterodyne detector technology lends itself naturally to spectroscopy so each band can be split into many sub-bands without loss of sensitivity‏
- Disadvantages:
- Fourier filtering of **large-scale** SZ signal (hence ALMA not really suitable for the large-scale emission)‏

## Foveated array benefits from MMIC arrays

- Several arrays with different primaries beams, with arrays on the larger dishes to match the field of view
- Small dishes target large angular scales
- Large dishes target small angular scales
**Equip the larger dishes with small arrays to match fields of view and increase mapping speed**
- Reduces correlator requirements
- Example 1m dish at 90 GHz has ~15’ primary beam
- 1000 sq m collecting area requires ~ 10^7 correlations
- But 100 1m dishes + 100 3m dishes  where each 3m dish has 7 pixels, has 800 detectors, but requires ~ few x 10^5 correlations

## A 6hr 90 GHz map made with such an interferometer

- Input, no sources (highly idealized cluster!)

- Output

- Combine with ALMA for even higher resolution

## Summary

- Technology developments
- Low noise MMIC amplifiers (few x quantum)‏
- Scalable array technology
- Development of large correlators
- Time is right to consider large-format millimeter-wave interferometers matched to particular science goals
- Take advantage of the versatility of coherent technology (Ekers talk)‏
- Interferometry
- Spectroscopy

## CHIP/MAS/SZI Working Groups

- Stanford
- Sarah Church
- Judy Lau
- Matt Seith
- Patricia Voll
- SLAC
- Sami Tantawi
- Dan Van Winkle
- John Fox
- Berkeley
- Dan Werthimer
- Don Backer
- NRAO
- Brian Mason
- Matt Morgan
- Steve Myers

- JPL
- Todd Gaier
- Pekka Kangaslahti
- Charles Lawrence
- Ian O'Dwyer
- Lorene Samoska
- Mike Seiffert
- Caltech
- Tony Readhead
- Tim Pearson
- Keiran Cleary
- University of Maryland
- Andy Harris
- Chicago
- John Carlstrom
- Erik Leitch

- University of Manchester
- Lucio Piccirillo
- Peter Wilkinson
- Cambridge University
- Keith Grainge
- Paul Alexander
- Mike Hobson
- Anthony Lasenby
- Oxford University
- Mike Jones
- Christian Holler
- Angela Taylor
- CITA
- Dick Bond
- Jon Sievers
- Laboratoire APC/CNRS
- Ken Ganga
- Jean-Paul Christoph