Astronomical instrumentation

Abstract:

It is well known that the clustering of galaxies depends on galaxy type. Such relative bias complicates the inference of cosmological parameters from galaxy redshift surveys, and is a challenge to theories of galaxy formation and evolution. In this paper we perform a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, η, as early- or late-type galaxies. We fit three different models of relative bias to the joint probability distribution of the cell counts, assuming Poisson sampling of the galaxy density field. We investigate the non-linearity and stochasticity of the relative bias, with cubic cells of side 10 ≤ L ≤ 45 Mpc (h = 0.7). Exact linear bias is ruled out with high significance on all scales. Power-law bias gives a better fit, but likelihood ratios prefer a bivariate lognormal distribution, with a non-zero 'stochasticity', i.e. scatter that may result from physical effects on galaxy formation other than those from the local density field. Using this model, we measure a correlation coefficient in log-density space (rLN) of 0. 958 for cells of length L = 10 Mpc, increasing to 0.970 by L = 45 Mpc. This corresponds to a stochasticity σb/b̂ of 0.44 ± 0. 02 and 0.27 ± 0.05, respectively. For smaller cells, the Poisson-sampled lognormal distribution presents an increasingly poor fit to the data, especially with regard to the fraction of completely empty cells. We compare these trends with the predictions of semi-analytic galaxy formation models: these match the data well in terms of the overall level of stochasticity, variation with scale and the fraction of empty cells.

Abstract:

The ClOVER instrument (described elsewhere in this volume) is being built to measure the B-mode polarisation of the Cosmic Microwave Background. Each of the 256 pixels is made up a pseudo-correlation receiver that can be realised using either waveguide or microstrip technology. In this work we present a design study for a possible waveguide-based solution. Each of the individual components has been optimised using electromagnetic finite-element modelling software (HFSS).

Abstract:

We present a new, fully-funded ground-based instrument designed to measure the B-mode polarization of the Cosmic Microwave Background (CMB). The concept is based on three independent subsystems operating at 90, 150 and 220 GHz, each comprising a telescope and a focal plane of horn-coupled background-limited bolometers. This highly-sensitive experiment, planned to be based at Dome C station in Antarctica, is optimised to produce very low systematic effects. It will allow the detection of the CMB polarization over angular multipoles 20 < l < 1000 accurately enough to measure the B-mode signature from gravitational waves to a lensing-confusion-limited tensor-to-scalar ratio r similar to 0.005.