The Square Kilometre Array (SKA)

Abstract:

We compare the environmental and star formation properties of far-infrared detected and non-far-infrared detected galaxies out to z ~ 0.5. Using optical spectroscopy and photometryfrom the Galaxy And Mass Assembly (GAMA) and Sloan Digital Sky Survey, with farin frared observations from the Herschel Astrophysical Terahertz Large Area Survey (ATLAS)Science Demonstration Phase, we apply the technique of Voronoi tessellations to analyse the environmental densities of individual galaxies. Applying statistical analyses to colour, r-band magnitude and redshift-matched samples, we show that there is a significant differenceat the 3.5σ level between the normalized environmental densities of these two populations. This is such that infrared emission (a tracer of star formation activity) favours underden seregions compared to those inhabited by exclusively optically observed galaxies selected to beof the same r-band magnitude, colour and redshift. Thus, more highly star-forming galaxiesare found to reside in the most underdense environments, confirming previous studies thathave proposed such a correlation. However, the degeneracy between redshift and far-infraredluminosity in our flux-density-limited sample means that we are unable to make a strongerstatement in this respect. We then apply our method to synthetic light cones generated fromsemi-analytic models, finding that over the whole redshift distribution the same correlations between star formation rate and environmental density are found. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

Modern ground-based radio-telescopes have stringent requirements on the receiver's feed-horn performance. These include a bandwidth covering a full atmospheric window from good sites (∼ 30%), low cross polarization and high beam circularity. In addition the unprecedented sensitivity required by recent proposed experiments requires large format focal plane arrays consisting of a large number of high performance feeds. While these feeds are straightforward to fabricate at microwave frequencies, the tight tolerances required in the THz region makes the realization of a large format array both expensive and time consuming. In this paper we describe feed designs that can be fabricated cheaply and rapidly without compromising the science requirements within the operating bandwidth. We present simulated and measured far-field beam patterns showing low sidelobe levels, good beam circularity and low cross-polarization levels over a fractional bandwidth of 20%. Having demonstrated the efficacy of our horn designs and fabricating technique experimentally, we have designed, fabricated and tested a prototype focal plane array of 37 hexagonally close packed horns milled in a single block of aluminum. Experimental testing of the radiation patterns of the array feeds demonstrated that they were essentially identical to the patterns of the feeds fabricated individually and that cross coupling between adjacent feeds was negligible. © 2013 IEEE.