North America Array: A Proposed Implementation of SKA-High

The North America Array is a concept for the implementation of the high-frequency component of the Square Kilometre Array, widely referred to as SKA-high. A high-level summary of the North America Array can be found in a recent presentation to the US SKA Consortium. The North America Array will be a continent-wide array of telescopes operating at short centimeter wavelengths that will provide images of unprecedented resolution and sensitivity. It will be built upon the capital investments of $500 million (FY09 dollars) in the Expanded Very Large Array (EVLA) and Very Long Baseline Array (VLBA), together with new technologies. It is envisioned that the first steps toward the North America Array, primarily technology development and prototyping of at least one antenna station, will be taken during the decade of 2010-2020. The final telescope will be built in the decade after 2020. The North America Array will continue the vision expressed in the EVLA Phase 1 proposal submitted to the National Science Foundation in 2000, but with considerably different implementation than was envisioned a decade ago. Quoting from the EVLA-I proposal (page 20):

In order to obtain sufficient angular resolution to avoid confusion at the high source densities expected for nanoJansky radio sources, and to adequately image distant galaxies, overall array dimensions of hundreds to thousands of kilometers, depending on wavelength, will be necessary. Because these are the dimensions of the EVLA, [nb. This included the New Mexico Array part of EVLA, which has not been funded.], it will constitute a critical first step towards the Square Kilometer Array. Possible next steps would be to extend the real-time operation of the New Mexico Array to the other eight elements of the VLBA, then to add large collecting areas at each of the VLBA and New Mexico Array sites using newly developed technology, and even to construct sites located on other continents. In this way it will be possible to approach the full capability of the SKA in a deliberate fashion, and at the same time maintain the viability of the user community during the long development and construction period of the SKA, which may extend over several decades.

1. Imaging thermal radio sources such as protoplanetary disks at resolutions of a few milliarcseconds (10 AU or better for nearby star-forming regions) and sensitivities well below a microJy
2. Imaging galaxies in the early universe, both active and non-active, to explore the evolutionary relationship between active and "non-active" galaxies.
3. Elucidation of the structure of the Galaxy and the Local Group through precision astrometry.
4. Determination of cosmological parameters and high-accuracy black-hole masses through astrometry of galaxies containing H₂O megamasers.

Several steps will be needed to implement the North America Array; these are listed below, with indications of what can be done in the coming decade and after 2020.

• Develop and test cost-effective technology for acquiring, transporting, and processing data from a greatly increased collecting area in the wavelength range from 0.6 cm through (at least) 10 cm (TDP-II program in 2012-2015)
• Build and test a prototype SKA-high antenna station, at a distance of (at least) hundreds of kilometers from the EVLA (2016-2019)
• Increase the sensitivity of the core EVLA (baselines up to tens of kilometers) by a factor of 5 (after 2020)
• Add sensitivity equivalent to 2-3 times the current EVLA at distances ranging from the EVLA maximum baseline of 35 km out to a few hundred kilometers (after 2020)
• Through the VLBA2010 program, increase the sensitivity of the current VLBA stations by increasing their bandwidths to near the 8 GHz per polarization of the EVLA (in 2010-2020)
• Enhance the long-baseline sensitivity of the North America Array by augmenting or replacing the VLBA stations with sensitivity equivalent to 2-3 times the current EVLA, most likely with arrays of smaller dish antennas (after 2020)
• Connect additional antennas to the EVLA in real time, beginning with the Pie Town VLBA antenna (part of the EVLA2010 program) and working outward as additional collecting area is being developed (Pie Town in 2010-2020, other stations as feasible)

Sub-components of the North America Array development are listed in the web links given on the left-hand menu bar.

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