* Astronomy

Title: Omniscopes: Large Area Telescope Arrays with only N log N Computational Cost
Authors: Max Tegmark (MIT), Matias Zaldarriaga (IAS)

We show that the class of antenna layouts for telescope arrays allowing cheap analysis hardware (with cost scaling as N log N rather than N^2 with the number of antennae N) is encouragingly large, including not only previously discussed rectangular grids but also arbitrary hierarchies of such grids, with arbitrary rotations and shears at each level. We show that all correlations for such a 2D array with an n-level hierarchy can be efficiently computed via a Fast Fourier Transform in not 2 but 2n dimensions. This allows major cost reductions for science applications requiring sensitivity at widely separated angular scales, for example 21cm tomography (where short baselines are needed to probe the cosmological signal and long baselines are needed for point source removal). Such hierarchical grids combine the angular resolution advantage of traditional array layouts with the cost advantage of a rectangular Fast Fourier Transform Telescope. We also describe an algorithm for how a subclass of hierarchical arrays can efficiently use rotation synthesis to produce global sky maps with minimal noise and a well-characterised synthesised beam.

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