SKA: Square Kilometer Array

Link to US SKA Web site

I. General project/facility description

1. Overview of the facility/project
   The Square Kilometer Array is an international project that will be the next generation centimeter-wavelength radio telescope. It will combine a two order of magnitude increase in sensitivity over existing array telescopes combined with widefield survey capabibility for continuum sources, spectral sources, and time variable sources. The specifications include high polarization purity, agility in sampling the time and frequency domains, and a total frequency range of 0.1 to 25 GHz. It will be a premier discovery instrument at flux density levels below one micro Jy and it is being designed to answer key questions in physics, astrophysics and astrobiology.
   In the US, as in several other countries, conceptual design work and technology development is proceeding in order to propose a specific architecture for the SKA to the international SKA project. The US concept is the "Large-N/Small-D" approach that involves a large number of relatively small-diameter paraboloids, and which we refer to as the LNSD concept. Preliminary analysis suggests D ~12m and N~4400. This work has been supported by an NSF Advanced Technology and Instrumentation grant (2002-2005) along with in-kind contributions from a number of universities and laboratories. A new proposal has been submitted to the NSF for a 5-year Technology Development Project (TDP) whose goal is to define a reference design for the SKA based on the LNSD concept for presentation to the international project and to the next decadal survey.
   The broad milestones for the SKA project include site selection and concept identification later this decade; prototype and demonstrator arrays late this decade and early next decade; construction proposals submitted to multiple national agencies early next decade; construction of the full array commencing in the middle of next decade; and completion with full operations by 2020.
   In addition to this linear plan for the SKA, it is recognized by many that it is both possible and desireable to reap scientific benefits from SKA technologies long before the full SKA is built. Consequently, plans are being discussed for demonstrator arrays to be built as soon as possible, both technically and financially.

2. Managing institution and organization
   The international SKA project is led by the International SKA Project Office (ISPO), currently at ASTRON (Netherlands) with R. Schilizzi as Project Director and P. Hall as Project Engineer. The ISPO is funded by contributions from international partners in the project, who are represented on the International SKA Steering Committee (ISSC). Currently there are 21 voting members of the ISSC, 7 of them from the US. This level of membership reflects the working plan that the US will ultimately contribute 1/3 of the construction and operations funds to the project. Standing committees for the project include a Site Evaluation and Selection Committee, a Science Working Group, an Engineering Working Group, an Outreach Committee, and about half a dozen subcommittees of these groups.
   The ISSC has laid out a time line for the project that includes (at present) site selection in 2006 and concept downselect in 2008. Countries that have submitted letters of intent to host/site the SKA are Australia, Argentina/Brazil, China, South Africa, and the US. It is expected that only a subset of these will submit formal siting proposals in 2005 for the decision milestone in 2006. Concepts now being pursued (after some initial winnowing that has taken place over the last few years) include: the LNSD concept (US, Australia, India), cylindrical reflectors (Australia), Arecibo-like reflectors (China), and phased arrays (Europe). Technology development is taking place on all concepts through resources garnered in individual countries.
   In the US, SKA efforts are organized through the US SKA Consortium (USSKAC), an organization of 17 universities and institutes that have signed a Memorandum of Understanding, first in 1999 and renewed in late 2004.

3. Funding source(s)
   Future facility: NYA
   The existing NSF/ATI grant is to Cornell University with J. Cordes as PI and the TDP proposal, also submitted on behalf of the USSKAC, is through NAIC/Cornell with J. Cordes as PI, and P. Goldsmith (Cornell), R. Cappallo (Haystack), S. Weinreb (Caltech), and J. Welch (UCB) as co-PIs. The TDP is under review by the NSF and we expect results after the Senior Review by the NSF of astronomy facilities and projects in late spring/early summer 2005.

4. Construction history and cost
   Future facility: NYA
   Estimated cost: (need quote)

5. Operational history and cost
   Future facility: NYA
   Estimated cost: (need quote)

II. Technical details

1. Specifics of telescope/instrument
   Future facility: NYA
   In the US current work on the LNSD concept is embodied in the Allen Telescope Array (SETI Institute, UC Berkeley) and the DSN array (JPL), along with strong synergies with the EVLA project. The TDP proposal mentioned above aims to consolidate this work and also commit resources to the development of inexpensive reflector manufacturing technology, wideband feeds and receivers, RFI mitigation techniques, and wide-field imaging in the large-N concept.

2. New capabilities anticipated/planned in next 5-10 years
   Future facility: NYA
   The preliminary specifications for the SKA flow down from five key science areas that delineate frontiers in astronomy and astrophysics and which aim to answer fundamental questions in both basic physics and in the complexity of the universe, including the formation of planets and life. These five areas map into frequency ranges as follows:

   Dark Matter, Dark Energy & Galaxy Evolution z < 2 HI surveys weak lensing continuum surveys	0.4 to 1.4 GHz 1 to 5 GHz
   Probing the Dark Ages HI/EoR: 6 < z < 13 CO: z > 6 AGNs:	0.1 to 0.2 GHz up to 25 GHz continuum to 8 GHz?
   Cosmic Magnetism Faraday rotation	0.3 to 10 GHz
   Gravity: Pulsars & Black Holes Galactic disk: Galactic center:	0.3 to 2 GHz 8 to 15 GHz
   Cradle of Life Protoplanetary disks: ISM molecules: SETI:	> 20 GHz 1 to 25 GHz 1 to 11 GHz

III. User profile

1. % of "open skies" time
   Future facility: NYA.

2. Institutional affiliations of users
   Future facility: NYA.

3. Student access, involvement, usage
   Future facility: NYA.

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
   
   • "Dark Matter, Dark Energy and Galaxy Evolution" involves massive surveys (10⁸ to 10⁹ sources) in HI up to redshifts ~2 and in continuum for weak and strong-lensing studies. These will yield constraints on the dark energy equation of state parameters, w₀ and w₁, of a few percent or better.
   • "Probing the Dark Ages" includes detection and analysis of the epoch of reionization signal imprinted in the redshifted 21cm line of hydrogen by the first sources of light, stars and black holes. It also includes detection of CO from high redshift sources that complement samples that will be studied with ALMA. The first active galactic nuclei may be detected through deep surveys that reach source thresholds of 10 to 100 nano Jy.
   • "Cosmic Magnetism" is an enterprise unique to radio astronomy: measurement of a large sample of Faraday rotation measures (10⁸) extragalactic sources, which can be converted into a three dimensional picture of magnetic fields vs. cosmological epoch.
   • "Gravity: Pulsars and Black Holes" addresses another key question posed in the report "Connecting Quarks with the Cosmos:" Was Einstein Right About Gravity? The SKA can conduct a nearly complete census of the 20,000 or so active radio pulsars in the Galaxy whose beams point toward Earth. Among these are rare binary pulsars having companion objects that include other neutron stars and black holes. Those with orbital periods of a few hours or less are especially good laboratories for testing theories of gravity in the strong-field limit. Deep surveys of the Galactic center are likely to find pulsars orbiting Sgr A* which may be especially lucrative in testing gravity in the vicinity of a massive black hole.
   • "The Cradle of Life" involves three subareas pertaining to the origins and detection of extrasolar life: comprehensive surveys of interstellar molecules, high-resolution imaging of protoplanetary disks, and SETI. With an appropriate configuration and coverage of high frequencies, the SKA can image disks in which Earth-like planets have carved out gaps. Such imaging can track the motions of such objects as they orbit their host star.

5. Synergies with other major forefront facilities
   {Part to add here (mph)}

6. Unique contributions
   Through considerations of the observational phase space that the SKA must cover to accomplish key science areas, that the SKA will be a transformational discovery instrument. It will have the time-domain capabilities of Arecibo, which has been prolific in discovering and analyzing pulsars, and the imaging capabilities of the VLA, but with 20 and 50 to 100 times the sensitivity of Arecibo and the VLA.

V. Education/Outreach activities

1. Visitor facility
   Future facility: NYA.
   Promotion of the SKA project is taking place at all levels. SKA booths have been placed at IAU meetings and AAS meetings. Public lectures on current science topics are given as evening activities associated with international SKA meetings that take place yearly. Science working groups have held open workshops over the last few years to attract new people to the project.
   EPO is a major part of the US TDP proposal. We have proposed to outfit about half a dozen universities with small radio antennas, receivers and spectrometers that will allow them to use some of the broadband technology we are developing for the project. These are intended for undergraduate laboratory components to courses in astronomy and which will provide hands-on access to radio telescopes. We also propose to install similar facilities at about half a dozen science and visitor centers, including the Ithaca Science Center, the Wisconsin Space Place, the Allen Telescope Array Visitor Center, and two others. These would be used to inform the public about the hydrogen spectral line at 21 cm and shared use of the radio spectrum by radio astronomers and others. This real-time display would be accompanied by an exhibit that used key science areas for the SKA to inform the public about how new technology is being used to confront fundamental questions about the origins of the universe and life and how radio techniques fit into others that are used across the electromagnetic spectrum.

2. Student programs
   Future facility. See above.

VI. Documentation/website URLs

1. URL of facility website
   
   • http://www.skatelescope.org: International SKA website.
     This site includes the scientific case for the SKA as it is currently envisioned, scientific and technical memos, white papers, and organizational material for the project.
   • http://www.usska.org: US SKA website.
     The US SKA Consortium's web site includes material particular to the Consortium and to the US concept that is not contained on the international site.

2. URL of EPO website
   Future facility: NYA.

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

4. URL(s) of miscellaneous documentation
   See above.