CARMA: The Combined Array for Research in Millimeter Wave Astronomy

Link to CARMA Web site

I. General project/facility description

1. Overview of the facility/project
   CARMA combines Caltech's and BIMA's (Berkeley Illinois Maryland Association) millimeter-wave arrays on a new, higher site. It is expected that CARMA, operating on a site with improved atmospheric transmission, with increased collecting area, much enhanced uv coverage, and enhanced electronics, will provide sensitivity at 1 mm that is an order of magnitude better than the exisiting arrays. We anticipate that U Chicago's Sunyaev Zel'dovich array (SZA) will become an integral part of CARMA in 2007, after initially independent operation on Cedar Flat.
   CARMA is currently (2005) being developed and constructed at the new site, Cedar Flat, at 7200 ft elevation in California's Inyo Mountains, and about 30 minutes drive from Owens Valley Radio Observatory.
   The new CARMA facility will replace the older facilities, namely, the Owens Valley Millimeter Array and the BIMA Millimeter Array at Hat Creek

2. Managing institution and organization
   CARMA will be managed by an association of the BIMA universities (UC Berkeley, U Illinois, U Maryland) and Caltech. The CARMA Board of Representatives has overall authority and responsibility for fiscal oversight, long-term policy, operation and management of the CARMA Association. A Science Steering Committee consisting of 8 scientists from the member universities provides advice. The Project Director coordinates the operation, oversight, and management of CARMA, as well as implementing the policies and decisions of the Board in consultation and coordination with the Science Steering Committee.
   Under a separate Memorandum of Understanding between the University of Chicago and Caltech, the SZA is currently being constructed at OVRO and will eventually be integrated into CARMA. To this end, negotiations between Caltech and Chicago are underway. When these are completed, the University of Chicago will join the CARMA Association and be allotted a seat on the Board, while one of the Caltech slots on the SSC will be officially allotted to Chicago. In practice, the SZA P.I., John Carlstrom, already participates actively in SSC deliberations.

3. Funding source(s)
   Capital construction costs for CARMA are estimated at $15M, of which NSF is contributing 1/3. The Caltech contribution derives from private funds while that from the BIMA partners relies on state funding from California, Illinois and Maryland.
   Discussions among the partner universities about combining the BIMA and OVRO arrays have been underway for more than five years. Some private/state funds were made available as early as 2000, and in that same year NSF provided seed money to support a project manager. Further NSF funding was assigned through a Major Research Infrastructure (MRI) grant in 2001. The balance of the remaining NSF capital contribution was awarded as part of the response to the CARMA Collaborative Research Proposal submitted in 2002.

4. Construction history and cost
   All potential CARMA sites were on U. S. Forest Service land, and considerable expense, time, and effort had to be devoted to the environmental permitting process. Cedar Flat was finally awarded in January 2004. Permission to develop the site took a few months longer. Nevertheless, the central array site is now cleared and 25 pads for the more compact array configurations are in place, as is associated trenching. Foundations for the three major buidlings have been poured. The nine BIMA pedestals and reflectors arrived on site in October/November of this year and now await newly-designed bases. The OVRO antennas are being upgraded at the old site since there is as yet no power at Cedar Flat. They should be moved in March/April. Despite the delays in the permitting process and in site development, we anticipate that CARMA will be operating - although perhaps only on a shared risk basis - by the end of 2005. At that time, pads with associated fiber and power will be available for the C, D, and E arrays. The more extended A and B arrays will become available later in 2006.

5. Operational history and cost
   Routine operation of the array should be possible in a limited number of modes in spring, 2006. Since their inception, the BIMA and OVRO arrays have been supported by operations funding from the NSF, supplemented by the respective states (Berkeley, Illinois, Maryland) and by private sources (Caltech). It is anticipated that this will be the operational model for CARMA.

II. Technical details

1. Specifics of telescope/instrument
   CARMA consists of a hybrid array combining the six 10.4-m antennas from OVRO with nine 6.1-m antennas from BIMA, operating at wavelengths from 1 to 10 mm (in future 0.8 to 10 mm).

2. New capabilities anticipated/planned in next 5-10 years
   Discussions among the partners about desirable capability improvements are now (Jan 2005) underway. Increased sensitivity and resolution are the driving requirements with a concomittant enhancement of correlator power. It will also be important to exploit the unique capabilities of the 23-element heterogeneous array. Dual polarization capability, on the fly mapping, dedicated single dish capability, and the addition of 1 mm receivers to the SZA complement, are also being considered.

III. User profile

1. % of "open skies" time
   Caltech and BIMA have always made a significant fraction of the observing time on their arrays available to the community at large. CARMA will continue this practice. As a result of discussions between NSF and the university partners, it is expected that approximately one third of the time will be "open skies."

2. Institutional affiliations of users
   Over the years, colleagues from numerous institutions across the United States, as well as an international subset, have made good use of the BIMA and OVRO arrays. We anticipate that CARMA users will come from these same groups but also expect that the enhanced capabilities may attract a broader community. For example, the discovery of the so-called "sub-millimeter galaxies" was already bringing in OVRO proposals from optical astronomers.

3. Student access, involvement, usage
   Time allocation on both the BIMA and OVRO arrays relied on peer review and scientific merit. We expect to apply the same standards to CARMA proposal evaluation. That said, we emphasize that student theses and post-doctoral research are very important to the university partners. We regard it as of prime importance that students in particular are assigned sufficient observing time for approved thesis projects. As part of the educational process, students and postdocs at the partner universities have always taken a large measure of the responsibility for day-to-day array operations and we expect that to continue. Over the years, we have also provided thesis observing time for students from universities other than the original CARMA partners and expect to continue that practice, assuming that there is appropriate support from their advisors.

IV. Science Overview

1. Current forefront scientific programs Future facility.

2. Major discoveries (through 1999)
   CARMA's promise has its foundation in the scientific discoveries with the BIMA and OVRO arrays over the years. Interferometric imaging at millimeter wavelengths has opened up a many new research areas of star formation and galaxy evolution, especially when coupled with infrared observations from IRAS, the Kuiper Airborne Observatory, and optical observations from HST and ground based telescopes. In fact, these highlights represent a summation of the major discoveries from "all years" . Every 3-year proposal from Caltech and BIMA to NSF has included major breakthroughs. Suffice it to say that the justification for ALMA (at that time called the Millimeter Wave Array) provided in the "Bahcall Report" - the decade survey for the 1990's presented, and relied heavily on, early OVRO and BIMA array results.

3. Science highlights of last 5 years
   These results from OVRO/BIMA:
   • First measurement of the dark matter distribution at the centers of dwarf galaxies at 100 pc resolution.
   • Continuum detection of the new class of high-redshift sub-millimeter galaxies.
   • Large surveys of molecular gas in the disks and nuclei of normal, active and starbust galaxies at 100-300 pc resolution
   • Imaging of the Sunyaev-Zel'dovich Effect and a determination of H_o and Ω
   • Detection of arcminute-scale Cosmic Microwave Background (CMB) anisotropy.
   • First complete survey of Giant Molecular Clouds (GMCs) in a spiral galaxy (M33).
   • Discovery of a short-lived, intermediate stage of disk formation in protostars.
   • Imaging of ring-arcs in the dust distribution around Vega.
   • Evidence for an HL Tau companion at the edge of the 0.2 arcsec resolution disk.
   • Measurement of polarization of thermal molecular lines of CO.
   • Detection of prebiotic molecules in hot molecular cores in the Galactic disk.
   • Imaging the weather on Titan.

4. Main future science questions to be addressed
   At the high altitude site, the most immediate improvement will be the ability to observe routinely at short wavelengths (1 mm). The enhancements in sensitivity, image fidelity, and bandwidth over what is possible at either existing array will make a whole new range of science available. A few possible projects include:
   • Wide area surveys of faint objects, such as high-redshift sub-millimeter galaxies which probe early galaxy evolution.
   • By probing large numbers of protostellar disks over a wide range of ages and environments, we will dramatically increase our understanding of how planetary systems evolve.
   • We will measure GMCs in Local Group galaxies to a resolution of about 2 pc, and resolve GMCs in a wide variety of more distant galaxies.
   • With the SZA as part of CARMA, we will refine measurements of the cosmological constant.

5. Synergies with other major forefront facilities
   The accessibilty of routine, high resolution 1 mm imaging will be important for complimentarity with space missions such as HST and Spitzer, and ground-based facilities such as SMA, LST, Keck and Gemini.
   During the years it will take to construct ALMA, CARMA will play a pathfinder role for mm-wave science, instrumentation, and imaging techniques. Once ALMA comes on-line, CARMA will serve as a test bed for potential ALMA upgrade technologies. The continuing success of ALMA will depend on a steady influx of inspired, capable, and experienced young people, many of who will come from the CARMA group.

6. Unique contributions
   
   • CARMA provides the US university-based, northern hemisphere, hybrid configuration complement to ALMA, as noted distinctly in the 2000 AASC Panel Report.
   • CARMA will be the first heterogeneous millimeter array, combining antennas of different sizes into a single powerful imaging instrument. This novel design combines the small antennas' view of large regions of the sky with the large antennas' sensitivity to very faint objects, allowing precise imaging of the Universe over a wide range of scales.

V. Education/Outreach activities

1. Visitor facility
   Both OVRO and Hat Creek Observatory (HCO) play important roles in education and outreach in the local community, giving tours, holding open houses, visiting local schools, writing newspaper articles, working with local educators at the K-12 and college level, mentoring local high school students, etc.
   On behalf of CARMA, Caltech is discussing joining a planned interagency visitor center for the Owens Valley. This would include displays highlighting the contribution of astronomy to science, technology and education. Being part of this center would provide a high-visibility focus for the array. A CARMA brochure suitable for the visitor center already exists.

2. Student programs
   University facilities provide an ideal environment for graduate students and postdoctoral fellows to acquire hands-on observing experience and instrument development skills while making exciting scientific discoveries. The most notable achievements at BIMA and OVRO have usually involved young researchers. During the past three years, at least 18 Ph.D. theses were based in large part on array observations. CARMA will build on these successes. More than a dozen professorial faculty are committed to the project, and the enhanced capabilities of the new array will attract high-quality students and postdocs. The latter will, as now, be awarded most of the observing time and be responsible for the bulk of the observing with the array. The experience so gained -- especially in trouble-shooting and other forms of advanced problem-solving -- is unique, and carries over to other endeavors.
   As part of formal training, the BIMA summer school is held annually at Hat Creek Radio Observatory (HCRO: the BIMA array site). This provides intensive hands-on training in mm-wave radio astronomy concepts, equipment and techniques. During the past three years, 45 people have attended, coming from 11 institutions: ASIAA (Taiwan), NAIC, CfA, Fed. U. Brazil, U. Illinois, U. Maryland, U. New Mexico, U. Chicago, U. Wisconsin, Shasta College and UC Berkeley. The summer school is always filled to capacity, and we plan to continue it.

3. Other (as apply)
   Members of BIMA and OVRO are active in Virtual Observatory (VO) initiatives, and we expect broader VO involvement through CARMA. The BIMA data archive and the Astrophysical Data Image Library (ADIL), developed and maintained by the BIMA Illinois group, are the foundation upon which the CARMA archive will be built, and already has many of the characteristics desired for the VO. Not only will the CARMA archive be the repository for raw data from the telescopes, it will also function as a digital library to support multi-wavelength science and archival research. Images from CARMA projects will become accessible via the archive to scientists from all disciplines and to the general public.

VI. Documentation/website URLs

1. URL of facility website
   Already BIMA, OVRO, and CARMA maintain active web sites for use by the community (see http:www.mmarray.org for links).