SZA: The Sunyaev-Zel'dovich Array

Link to SZA web site

I. General project/facility description

1. Overview of the facility/project
   The SZA is an eight element interferometric array of 3.5m diameter alt/az precision radio telescopes. The array currently operates in two frequency bands, 26-36 GHz and 85 - 115 GHz. A digital correlator provides 8 GHz of instantaneous correlation bandwidth.
   The initial observational goal of the SZA is to conduct a 12 square degree survey for distant galaxy clusters via the Sunyaev-Zel'dovich Effect, and to measure the CMB anisotropy power spectrum from multipoles of 1500 to several thousand. The initial survey and power spectrum will be done at 30 GHz, but each cluster detected will be followed up with pointed SZA observations at 90 GHz.
   After the initial SZE experiments the SZA will be fully incorporated into the CARMA array, making CARMA a 23 element, heterogeneous interferometric array. See the CARMA report.

2. Managing institution and organization
   The SZA is led by the University of Chicago under PI J. Carlstrom. It is a collaboration with Caltech and has collaborators at Columbia University and NASA/MSFC.

3. Funding source(s)
   The SZA is funded by NSF-AST ATI program at $2.8M, the NSF Center for Cosmological Physics at $1.7M and with over $2M from the University of Chicago and other private sources. An additional $0.7M is leveraged by utilizing existing cm-wave hardware at the University of Chicago.
   A proposal to the NSF AST ATI program will be submitted in Nov 2005 to fund the operations and science with the SZA from the end of the current grant period on 2006 April to the beginning of the next period of the CARMA NSF AST URO program in 2008 Nov. At that time the SZA will be fully integrated into CARMA and funding will be requested as part of the CARMA collaborative URO proposal.

4. Construction history and cost
   The SZA has accomplished first light and the full array is now undergoing engineering tests. Routine observations on the Owens Valley floor are slated to start this winter. The funds are detailed above. The SZA will move to the new high CARMA site when it is ready in 2005 Summer.

5. Operational history and cost
   New facility: NA.

II. Technical details

1. Specifics of telescope/instrument
   
   • Array elements:
     • 3.5 meter diameter with alt/az mount.
     • Aluminum high precision panels with typically 6 to 9 µ rms surface accuracy.
     • Overall surface budget is < 30 µ rms to allow high aperture efficiency when eventually operated at 300 GHz.
     • Novel design to allow close packing of the array with telescope spacings as short as 1.25 times the diameter of the primary reflector.
   • Receivers:
     • 26 - 36 GHz hybrid HEMT amplifier cooled receivers T(rx) ~ 10 - 15K SSB
     • 85 - 115 GHz MMIC HEMT amplifier cooled receivers T(rx) ~ 38 - 45 K SSB
   • Correlator:
     • new digital correlator technology based on FPGAs designed by D. Hawkins. Consists of sixteen 500 MHz bands, each one has 32 frequency channels when configurated for the broadest bandwidth. Correlator can be configured for higher resolution at cost of total bandwidth.
     • all tracking delays are implemented digitally.
   • Receivers, Electronics and Software are all designed to be compatible with CARMA.

2. New capabilities anticipated/planned in next 5-10 years
   It is planned to outfit the SZA with 1 mm receivers in the future for 1 mm heterogeneous array observations with CARMA. Dual polarization receivers for all bands is also being discussed.

III. User profile

1. % of "open skies" time
   The SZA will be a dedicated science experiment for the next ~3 years. The resulting data will be made public. After this period the SZA will become part of CARMA and follow its practices regarding public access (currently ~30% to outside users).

2. Institutional affiliations of users
   Currently, U. Chicago, Columbia University, Caltech, NASA/MSFC. See above.
3. Student access, involvement, usage
   The SZA is being built by students and will be used primary by graduates students for their Ph.D. thesis research. Currently there are 8 graduates students working on the project as well as several undergraduates students.

IV. Science Overview

1. Current forefront scientific programs
   The SZA is the forefront instrument for SZE research. It will provide the first catalog of SZE selected galaxy clusters. As the SZE is independent of redshift, the SZA survey will be the first catalog of high redshift, massive clusters.

2. Major discoveries (through 1999)
   New facility: NA.
3. Science highlights of last 5 years
   New facility: NA.
4. Main future science questions to be addressed
   The key science program of the SZA is a large-scale survey of the distant universe to search for the signature of the Sunyaev-Zel'dovich Effect and for anisotropy in the Cosmic Microwave Background. The SZA will survey 12 square degrees for distant galaxy clusters via their SZE.
   The SZA will determine the CMB power spectrum from multipoles of 1500 to several thousand. Currently power in excess of that predicted by the instrinsic CMB anisotropy has been detected at these angular scales. The signal is believed to be due to unresolved, diffuse SZE from distant clusters. If so, it will be highly sensitive to the mass density and its fluctuation spectrum. Another alternative is that the excess anisotropy power results from the first generation of stars. The SZA will characterize the power spectrum and with deep observations attempt to resolve the sources causing the excess power.

5. Synergies with other major forefront facilities
   The SZA initial SZE survey and its 90 GHz follow-up observations will provide a first SZE selected catalog for detailed cluster research, especially for understanding how to best use galaxy clusters for future surveys such as the SPT survey and those done at other wavelengths.

6. Unique contributions
   Due to its well understood, redshift independent and simple selection criteria, essentially simply a mass threshold, the SZA cluster sample will be the high redshift cluster sample of choice for several studies:
   • The density of clusters as a function of redshift will be determined. This information will allow tight constraints on the universal density parameter as well as the normalization of its variance.
   • Distance measurements at high redshift that are completely independent of other methods. Together with redshift information, this will provide a measure of Hubble constant as well as a means to confirm the determinations of the geometry of the universe found from Type 1a supernovae
   • Most importantly for future research using clusters of galaxies for cosmology, the SZA sample with detailed SZA+CARMA follow-up imaging will allow the physics and evolution of galaxy clusters to be studied in detailed and compared with simulations. In this sense the SZA is a pathfinder SZE instruments for future, extremely sensitive surveys that will survey 1000's of degrees but at limited angular resolution, such as the SPT SZE survey.
   When the SZA is combined with the CARMA telescopes, it will provide unprecedented observing opportunities. The primary instrumentation enhancements to CARMA by the addition of the eight SZA telescopes are:
   • An increase by a factor of two the largest angular scales to which CARMA is sensitive, resulting in a doubling of the angular dynamic range.
   • An increase in the number of baselines from 105 to 253, resulting in improved imaging fidelity.
   • An increase in the flexibility to use sub-arrays to conduct multiple science projects simultaneously.
   The enhancements stated above will provide increased scope over the broad spectrum of CARMA science, for example:
   • Cosmology and Large Scale Structure of the Universe. The Sunyaev-Zel'dovich Effect studies are an excellent example. The combination of the large angular scales provided by the SZA and the high point source sensitivity provided by the larger telescopes will make CARMA unsurpassed for SZE imaging of galaxy clusters. The heterogeneous array will also be ideally suited for measuring the fine angular scale anisotropy of the cosmic microwave background radiation (CMBR) caused by the SZE, the reionization history of the universe and the growth of large scale structure.
   • External Galaxies:   The increased angular scales, angular dynamic range and imaging fidelity will improve CARMA's ability to image the molecular and ionized gas of nearby galaxies. Such data will be used to investigate galactic dynamics and chemistry and to probe the underlying dark matter potentials.
   • Galactic Structure:   The increased angular scales, dynamic range and imaging fidelity will also improve CARMA investigations of the interstellar and molecular medium of the Milky Way. The lower frequencies can be used to trace the ionized components, such as supernovae remnant's and their impact on the molecular gas. The increase imaging capabilities will allow CARMA to better investigate the life cycle of molecular cloud complexes.
   • Star Formation:   A complete picture of star formation requires understanding the collapse of the molecular cloud on scales of parsecs to the formation of the star-disk system at scales of the solar system. The increased angular dynamic range will allow CARMA to image and investigate the dynamics and chemistry involved over this entire angular range.
   • Solar System:   The large angular scales provided by the 3.5 m telescopes will allow imaging of all the planets. The increased angular scales and in particular the increased imaging speed, fidelity and snapshot capabilities of CARMA will be extremely useful for observations of the thermal and molecular emission from comets.

V. Education/Outreach activities

1. Visitor facility
   The SZA will not be a visitor facility until incorporated into CARMA. At that time it will also participate fully the CARMA EPO programs.

2. Student programs
   As noted above, students (8 graduate students) and postdocs are constructing the lion share of the SZA. They are learning a great deal of hands-on experimental techniques. As the hardware is nearly complete, they are now concentrating on data reduction, observing and science. These students are receiving valuable (and unfortunately rare) training in radio astronomy techniques.

3. Other (as apply)
   The SZA hardware is being used in undergraduate education at the University of Chicago. The correlator technology has been used to build a spectrometer for the student laboratory HI 4.5 m telescope. The low-noise cm-wave receivers are used in the undergraduate CMB laboratory. All of the SZA graduate students participate in the laboratory setup and instruction.

VI. Documentation/website URLs

1. URL of facility website
   http://astro.uchicago.edu/sza/index.html

2. URL of EPO website
   

3. URL(s) of any brief overviews of project/facility
   

4. URL(s) of miscellaneous documentation
   See Carlstrom, Holder and Reese 2002 ARAA V40, 643 for review of Cosmology with the SZE.