The Square Kilometre Array (SKA)

Abstract:

We forecast the abilities of the Atacama Large Millimeter/submillimeter Array (ALMA) and the Square Kilometer Array (SKA) to detect CO and H I emission lines in galaxies at redshift z = 3. A particular focus is set on Milky Way (MW) progenitors at z = 3 since their detection within 24hr constitutes a key science goal of ALMA. The analysis relies on a semi-analytic model, which permits the construction of an MW progenitor sample by backtracking the cosmic history of all simulated present-day galaxies similar to the real MW. Results are as follows: (1) ALMA can best observe an MW at z = 3 by looking at CO(3-2) emission. The probability of detecting a random model MW at 3σ in 24hr using 75 km s-1channels is roughly 50%, and these odds can be increased by co-adding the CO(3-2) and CO(4-3) lines. These lines fall into ALMA band 3, which therefore represents the optimal choice toward MW detections at z = 3. (2) Higher CO transitions contained in the ALMA bands ≥6 will be invisible, unless the considered MW progenitor coincidentally hosts a major starburst or an active black hole. (3) The high-frequency array of SKA, fitted with 28.8GHz receivers, would be a powerful instrument for observing CO(1-0) at z = 3, able to detect nearly all simulated MWs in 24hr. (4) H I detections in MWs at z = 3 using the low-frequency array of SKA will be impossible in any reasonable observing time. (5) SKA will nonetheless be a supreme H I survey instrument through its enormous instantaneous field of view (FoV). A one-year pointed H I survey with an assumed FoV of 410 deg2 would reveal at least 105 galaxies at z = 2.95-3.05. (6) If the positions and redshifts of those galaxies are known from an optical/infrared spectroscopic survey, stacking allows the detection of H I at z = 3 in less than 24hr. © 2011. The American Astronomical Society. All rights reserved.

Abstract:

We describe an upgrade to the Cosmic Background Imager instrument to increase its surface brightness sensitivity at small angular scales. The upgrade consisted of replacing the 13 0.9-m antennas with 1.4-m antennas incorporating a novel combination of design features, which provided excellent sidelobe and spillover performance for low manufacturing cost. Off-the-shelf spun primaries were used, and the secondary mirrors were oversized and shaped relative to a standard Cassegrain in order to provide an optimum compromise between aperture efficiency and low spillover lobes. Low-order distortions in the primary mirrors were compensated for by custom machining of the secondary mirrors. The secondaries were supported on a transparent dielectric foam cone to minimize scattering. The antennas were tested in the complete instrument, and the beam shape and spillover noise contributions were as expected. We demonstrate the performance of the telescope and the intercalibration with the previous system using observations of the Sunyaev-Zel'dovich effect in the cluster Abell 1689. The enhanced instrument has been used to study the cosmic microwave background, the Sunyaev-Zel'dovich effect and diffuse Galactic emission. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.