Cosmology

Abstract:

Accurate calibration of data is essential for the current generation of CMB experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 percent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 percent precision. The sources for which a 1 percent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ~30 GHz is given for each. Cas A,Tau A, NGC7027 and Venus were examined for variability. Cas A was found to be decreasing at $0.394 \pm 0.019$ percent per year over the period March 2001 to August 2004. In the same period Tau A was decreasing at $0.22\pm 0.07$ percent per year. A survey of the published data showed that the planetary nebula NGC7027 decreased at $0.16\pm 0.04$ percent per year over the period 1967 to 2003. Venus showed an insignificant ($1.5 \pm 1.3$ percent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be $7.8\pm 0.6$ percent at pa $ = 148^\circ \pm 3^\circ$.}

Abstract:

We have carried out a concept study for a wide-field monolithic integral field unit (IFU) spectrograph for extremely large telescopes (ELTs). We target in this paper the technological challenges that have to be faced in order to build such an instrument, focusing on the adaptive optics (AO) requirements, the image slicer technology, and the detectors status. We also address the main science drivers, together with the concept design and the expected performance applied to the European-ELT (E-ELT) case. A monolithic wide-field spectrograph provides a continuous field of view (FOV) separated by a field splitter in several subfields, each of them feeding a module featuring an image slicer, a collimator and a spectrograph. The use of image slicers provides 3D spectrographic images of the complete FOV, allowing for detection and study of sources without need of targeting them, a very useful property especially for the deep observation of faint high-redshift objects, whose density on the sky is expected to be quite high. In light of this discussion, we suggest the advantages of using shorter wavelengths and its implication in both the scientific program and the budget. © 2008. The Astronomical Society of the Pacific. All rights reserved.

Abstract:

We have developed a semi-empirical simulation of the extragalactic radio continuum sky suitable for aiding the design of next generation radio interferometers such as the Square Kilometre Array (SKA). The emphasis is on modelling the large-scale cosmological distribution of radio sources rather than the internal details of individual galaxies. Here we provide a description of the simulation to accompany the online release of a catalogue of 320 million simulated radio sources. The simulation covers 20x20 deg^2 - a plausible upper limit to the instantaneous field of view attainable with future (e.g. SKA) aperture array technologies - out to redshift z=20, and down to flux density limits of 10 nJy at 151, 610 MHz, 1.4, 4.86 and 18 GHz. Five distinct source types are included: radio-quiet AGN, radio-loud AGN of the FRI and FRII structural classes, and star-forming galaxies, the latter split into populations of quiescent and starbursting galaxies. In our semi-empirical approach, the simulated sources are drawn from observed (or extrapolated) luminosity functions and grafted onto an underlying dark matter density field with biases which reflect their measured large-scale clustering. A numerical Press-Schechter-style filtering of the density field is used to identify and populate clusters of galaxies. Radio source structures are built from point source and elliptical sub-components, and for FRI and FRII sources an orientation-based unification and beaming model is used to partition flux between the core and extended lobes and hotspots. The simulation output can be post-processed to achieve more complete agreement with observational data in the years ahead, with the aim of using these 'idealised skies' in telescope simulators to optimise the design of the SKA itself (abridged).