ALMA: The Atacama Large Millimeter Array

Link to ALMA Web site

I. General project/facility description

1. Overview of the facility/project
   The Atacama Large Millimeter/Submillimeter Array (ALMA) is a revolutionary instrument in its scientific concept, in its engineering design, and in its organization as a global endeavor. ALMA will provide scientists with precise images of galaxies in formation, seen as they were twelve billion years ago; it will reveal the chemical composition of heretofore unknown stars and planets still in their formative process; and it will provide an accurate census of the size and motion of the icy fragments left over from the formation of our own solar system that are now orbiting beyond the planet Neptune. These science objectives, and many more, are made possible owing to the design concept of ALMA that combines the clarity of detail in images provided by a 64-antenna interferometric array together with the brightness sensitivity of a fully filled aperture.
   The challenges of engineering the unique ALMA telescope begin with the need for the telescope to operate in the thin, dry air found only at elevations high in the Earth's atmosphere where the light at millimeter and submillimeter wavelengths from cosmic sources penetrates to the ground. ALMA will be sited in the Altiplano of northern Chile at an elevation of 5000 meters (16,500 feet) above sea level. The ALMA site is the highest, permanent, astronomical observing site in the world. On this remote site superconducting receivers that are cryogenically cooled to less than 4 degrees above absolute zero will operate on each of the 64 12-meter diameter ALMA antennas. The signals from these receivers will be digitized and transmitted to a central processing facility where they will be combined and processed at a sustained rate greater than 10¹⁶ operations per second. As an engineering project, ALMA is a collection of 64 precisely-tuned mechanical structures each weighing more than 80 tons, cryogenically cooled superconducting electronics, and optical transmission of data at terabit rates--all operating together, continuously, on a site very high in the Andes mountains.
   The challenges of communicating the mission and the excitement of ALMA to the citizens who ultimately sponsor the project is a task as vital as the engineering challenges. To this end, a comprehensive program of education and public outreach is an integral part of the ALMA Project.

2. Managing institution and organization
   The Atacama Large Millimeter Array (ALMA) is an international astronomy facility. Today, ALMA is an equal partnership between Europe and North America, in cooperation with the Republic of Chile, and is funded in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC), and in Europe by the European Southern Observatory (ESO) and Spain. In the near future, the process whereby Japan becomes a participant in ALMA, adding a compact array and receiver bands, is expected to be completed. ALMA construction and operations are led on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) under a cooperative agreement with the NSF, and on behalf of Europe by ESO.
   • ALMA is organized between three partners: North America, Europe, and Japan. Chile is not a partner, but has representation in ALMA at all levels.
   • The ALMA Agreement, signed by the partner funding agencies, sets out the organizing principles and working arrangements between the partners.
   • ALMA is governed by a Board, with representatives from each of the partners. The current U.S. members are R. Dickman (NSF), F. Lo (AUI/NRAO), and A. Sargent (Caltech). J. Hesser (NRC) represents Canada.
   • The partners are committed to deliverables valued at 37.5%:37.5%:25% of the total value of the project, North America, Europe, and Japan, respectively. The split within North America is 93%:7% between the United States and Canada.
   • Each partner has designated an Executive to carry out that partner's responsibilities in ALMA; for North America, the Executive is AUI/NRAO.
   • ALMA construction activities are conducted by joint teams which report to the Joint ALMA Office.
   • Oversight is provided by the ALMA Management Advisory Committee and the ALMA Science Advisory Committee, both of which report to the ALMA Board.
   • The Executives have established their own advisory bodies for contact with their own communities, and they conduct their own education and outreach programs.

3. Funding source(s)
   
   • The sole funding source for the United States participation in ALMA is the National Science Foundation.
   • In Canada, the funding for ALMA comes from the National Research Council; in Europe, from the European Southern Observatory and Spain; in Japan, from the National Institutes of Natural Sciences.

4. Construction history and cost
   ALMA constuction began in 2002, following four years of design and development (funded under the MREFC line).
   US ALMA Construction Budget (Millions US$ Y2000)

   Design & Dev.	2002 actual	2003 actual	2004 actual	2005 actual	2006 est.	2007 est.	2008 est.	2009 est.	2010 est.	Total Const.
   32.0	12.0	28.1	42.2	41.5	39.2	37.1	34.8	27.0	14.3	276.3

   Status of major items:
   • Site: The ALMA site has been secured for 50 years with the signing of several official agreements with the Republic of Chile. The site is protected from harmful development by Presidential decree and from radio frequency interference by the establishment of a Quiet/Coordination Zone. An access road to the site has been cleared that will in time become a paved road to the mid-level facility where most staff will work and live with a wide, unpaved road from there to the site itself capable of carrying antenna transporters. A camp for ALMA staff has been constructed in temporary buildings at the mid-level location; a contractor's camp is being built. Antenna foundations will be installed on the high site in the (southern) summer of 2005-6. At the same time construction will start on aa building to house the correlator, with work space for a small crew, on the high site. Larger facilities at the mid-level location will follow (antenna assembly bays, laboratory and office space, power plant, etc.)
   • Antennas: Following testing of two prototype antennas, a call for bids for the production antennas was issued, bids were received and evaluated, and pending completion of negotiations with the winning bidder, a contract will be signed. The goal is to order all identical antennas in two contracts, one from NRAO/AUI and one from ESO.
   • Other components: Progress on the backend system, the correlator and computing are on schedule. Progress on front ends and systems engineering are slightly behind schedule but schedule should be recovered. A science verification plan has been produced to ensure that ALMA meets its scientific requirements.

5. Operational history and cost
   Future facility: estimate only.
   NRAO/AUI is proposing a program of user support for ALMA data analysis to the NSF, along the lines of the 2000 AASC report recommendations. ALMA is expected to produce ~100 Tbytes/year of data. This exceeds the total amount of data accumulated in the HST archive in its lifetime by a factor of five, every year. Users will require resources at their home institutions, as well as the services of the North American ALMA Science Center, if they are to reduce and analyze this data effectively.

II. Technical details

1. Specifics of telescope/instrument
   

   Array		Main	Compact(ACA)
   	Number of Antennas (N)	64	16
   	Total Collecting Area (p/4 ND2)	7238 m2	915
   	Total Collecting Length (ND)	768 m	132
   	Angular Resolution	0.2 arcsec λ(mm)/baseline (km)
   Array Configurations	(dimension of filled area)
   	Compact: Filled	150 m	35 m
   	Continuous Zoom	150-18500 m
   	Highest Resolution	14.8 km
   	Total Number of Antenna Stations	216	22
   Antennas
   	Diameter (D)	12 m	4 × 12m + 12 × 7m
   	Surface Accuracy	25 µ RMS	12m: 25µ; 7m: 20µ
   	Pointing	0".6 RSS in 9 m/s wind	same

   Front Ends
   (All frequency bands are dual polarization with noise performance limited by the atmosphere)
   • 84 - 116 GHz SIS ⁺
   • 125 - 163 GHz SIS^@
   • 211 - 275 GHz SIS ⁺
   • 275 - 373 GHz SIS ⁺
   • 385 - 500 GHz SIS^@
   • 602 - 720 GHz SIS ⁺
   • 787 - 950 GHz SIS^@
   • Water Vapor Radiometer: 183 GHz

   Intermediate Frequency (IF)
   	Bandwidth	8 GHz, each polarization
   Correlator		Main Array	Compact Array (ACA)
   	Correlated baselines	2016 (=64x63/2)	120
   	Bandwidth	16 GHz per antenna	same
   	Spectral Channels	4096 per IF	same
   Data Rate
   	Data Transmission from Antennas	120 Gb/s per antenna, continuous
   	Signal Processing at the Correlator	1.6 × 1016 multiply/add per second

   ⁺ Four frequency bands required for first-light ALMA. Receivers in six additional atmospheric winders are deferred to future development.
   ^@ Bands supplied by Japan for main array. Japan provides all bands for ACA.

2. New capabilities anticipated/planned in next 5-10 years
   New facility. Expected completion 2012, but partial array operations in 2008.

III. User profile

1. % of "open skies" time
   The North American scientific community will have access to 37.5% of ALMA time (assuming all current ALMA partners, including Japan, are able to meet their commitments to ALMA construction). This time will be distributed among principal investigators at institutions in the United States, Canada, and Mexico on an "open skies" basis. The other international partners will control access to their own shares.

2. Institutional affiliations of users
   The institutional distribution of users is expected to be at least as broad as it is at present for the VLA, except that users at European and Japanese institutions will have access to ALMA through their own ALMA Regional Centers. In a restricted call (ASAC, ALMA Science IPT, et al.) for sample proposals to be used in the Design Reference Science Plan for ALMA, 128 proposals were received from 75 investigators from a broad range of institutions.

3. Student access, involvement, usage
   Student access to ALMA time will be encouraged and supported, as it is for other NRAO telescopes.

IV. Science Overview

1. Current forefront scientific programs
   Future facility: NA

2. Major discoveries (through 1999)
   Future facility: NA

3. Science highlights of last 5 years
   Future facility: NA

4. Main future science questions to be addressed
   
   • Image the redshifted dust continuum emission from evolving galaxies at epochs of formation as early as z=10
   • Trace through molecular and atomic spectroscopic observations the chemical composition of star-forming gas in galaxies throughout the history of the Universe
   • Reveal the kinematics of obscured galactic nuclei and Quasi-Stellar Objects on spatial scales smaller than 300 light years
   • Image gas rich, heavily obscured regions that are spawning protostars, protoplanets and preplanetary disks
   • Reveal the crucial isotopic and chemical gradients within circumstellar shells that reflect the chronology of invisible stellar nuclear processing
   • Obtain unobscured, sub-arcsecond images of cometary nuclei, hundreds of asteroids, Centaurs, and Kuiper Belt Objects in the Solar System along with images of the planets and their satellites
   • Image solar active regions and investigate the physics of particle acceleration on the surface of the Sun.

5. Synergies with other major forefront facilities
   
   • Spitzer
     • ALMA's field of view is smaller than Spitzer's, but ALMA has much higher angular resolution. In this respect, Spitzer is a finding telescope for ALMA.
     • Spitzer identified infrared excesses around stars with ages up to 800 Myr and determined their short wavelength spectral energy distribution (SED); ALMA will detail the distribution of the cool matter in these spectral components, lifting the degeneracies involved with SED interpretation.
     • ALMA's spectral coverage is complementary to Spitzer's.
   • Herschel
     • There is considerable frequency overlap (H: 480-1910 GHz; ALMA 30-950 GHz), but orders of magnitude difference in spatial resolution (Herschel: 12"-40"; ALMA Interferometry: 0.005"-2").
     • Short wavelength coverage on Herschel's PACS and SPIRE instruments will define SEDs of isolated objects.
     • Herschel's lifetime is contemporary with ALMA Early Science 2007-2010.
     • Herschel's 75-517 µ sensitivity 1 sigma/1 hour = 1 mJy, whereas, for ALMA 1 sigma/1 minute = 1 mJy.
     • Herschel directly observes the key interstellar water molecule; ALMA will provide detailed images of the distribution of its (much less abundant) isotopomers.
   • James Webb Space Telescope
     • Formation of the Hubble Sequence:
       • OIR telescopes are sensitive to stars;
       • ALMA is sensitive to mass, and can separate the gravitational potential from luminosity burst, and hence, differentiate galaxies that are forming from both multiple sub-galaxies and from mergers of pre-existing galaxies.
   • WMAP/Planck
     • These space missions will measure the CMBR fluctuation spectrum, with the consequence that extensive ALMA programs will be needed to measure the evolution of structure as traced by the S-Z effect, and by galaxy and intergalactic gas distributions.
   • GSMT/TMT/GMT (Large Optical Telescope)
     • For the first time, a facility operating at mm wavelengths will provide sensitive observations of the cold, molecular universe at angular resolutions ~10 mas--nearly 100× that achievable today and 10× that of the Keck telescope.
     • Two hours' ALMA integration at 850 microns will reveal, on average, between one and two galaxies per pointing. For one of these, a CO spectral line will be detected within the ALMA IF, providing a redshift estimate.
     • At high redshifts (z ~ 6-9) CO line emission will migrate to lower frequencies as emission from [C II] and [N II] migrates from higher frequencies.
     • This is a sampling density of 10⁵ galaxies per square degree, of which ALMA will obtain redshift information for half. The equivalent of L* densities in the present-day universe will be probed at high redshift, and the properties of this millimeter-selected sample can be compared with an optical sample from the TMT, which will reach nearly the same surface density of galaxies.
     • High signal-to-noise TMT spectra can be used to estimate the metallicity of the gas and stars in galaxies at z > 3; for the brightest of these ALMA will provide some isotope information, yielding a clue to the nucleosynthetic history of the earliest stellar populations.
   • Expanded Very Large Array (EVLA)
     • While JWST traces luminosity and ALMA mass, the EVLA traces energetic particles associated with magnetic fields. Together these instruments provide a comprehensive picture of galaxies and their interactions.
     • For high redshifts (z > 4), the EVLA can be used to image CO emission from lower J transitions for comparison with the ALMA images of higher J transitions, yielding important information on excitation.
     • Imaging of HI distribution is complementary to imaging of molecular gas distribution by ALMA.
   • Green Bank Telescope/Large Millimeter Telescope (GBT/LMT)
     • Both the LMT and GBT can provide interesting targets for ALMA from their large area camera surveys;
     • The LMT and GBT can provide short spacing information for large area mapping projects ALMA may choose to do (at low frequencies and in the right part of the sky) before the time that ALMA operates with full total power capability and/or the Atacama Compact Array (ACA) (or should the ACA become needed for more than the planned 25% of ALMA projects).
     • The LMT and ALMA represent the two largest elements (thus account for most of the sensitivity) of the mm/submm VLBI network. For example, resolving the accretion disk/horizon of the SgrA* black hole or accretion disks of nearby AGNs will require both LMT and ALMA.

6. Unique contributions
   
   • The ability to detect spectral line emission from CO or CI in a normal galaxy like the Milky Way at a redshift of 3, in less than 24 hours of observation.
   • The ability to image the gas kinematics in protostars and protoplanetary disks around young Sunlike stars at a distance of 150 pc, enabling one to study their physical, chemical and magnetic field structures and to detect the gaps created by planets undergoing formation in the disks.
   • The ability to provide precise images at an angular resolution of 0.1". Here the term "precise images" means representing to within the noise level the sky brightness at all points where the brightness is greater than 0.1% of the peak image brightness. This requirement applies to all sources visible to ALMA that transit at an elevation greater than 20°.

V. Education/Outreach activities

1. Visitor facility
   Future facility: under development
   ALMA will have a Visitor center at the Operations Support Facility at 2900m altitude. The potential audience includes the 10000 visitors to San Pedro de Atacama per month during the austral summer, plus students from San Pedro, Calama and throughout Chile's Region II.

2. Student programs
   Summer student programs will include participation of ALMA in the programs run by NRAO for the last 45 years. There have typically been about 25 participants per year in the program, partially supported by the NSF REU program and partially supported by other NRAO funds.

VI. Documentation/website URLs

1. URL of facility website
   The ALMA website is located at www.alma.nrao.edu.

2. URL of EPO website
   Because ALMA is a construction project, on which expenditure of EPO funds is not allowed (by NSF MREFC rules), there is not now a specific ALMA EPO website. Some material may be found at: http://www.alma.nrao.edu/science/basics/index.html.

3. URL(s) of any brief overviews of project/facility
   Wootten's ALMA overview to the SPIE in July 2002: http://www.cv.nrao.edu/%7Eawootten/mmaimcal/spiealma2.pdf
4. URL(s) of miscellaneous documentation
   
   • Wootten's ALMA paper for the upcoming 2005 IEEE International Conference on Acoustics, Speech, and Signal Processing March 19-23 2005, Philadelphia; that paper is available at: http://www.cv.nrao.edu/~awootten/mmaimcal/ALMAOuterLimits.pdf.
   • A recent meeting on Herschel-ALMA synergies was held in Paris; some general ALMA articles submitted to the proceedings may be found at: http://www.cv.nrao.edu/~awootten/mmaimcal/DUSTY04Papers.pdf.
   • The ALMA Design Reference Science Plan may be inspected at: http://www.strw.leidenuniv.nl/~joergens/alma
   • The ALMA Project Book is available at: http://www.alma.nrao.edu/projectbk/construction/
   • The ALMA Science Case is available in ASP Conference Series Vol. 235 "Science with ALMA" and at http://www.eso.org/projects/alma/science/alma-science.pdf
   • Vanden Bout has written a brief history of the ALMA partnership and its roots in earlier projects (MMA, LSA, & LMSA) available as astro-ph/0411071