The C-Band All-Sky Survey (C-BASS): Design and capabilities

 

Authors: M.E. Jones, A.C. Taylor, M. Aich et al.
Journal: MNRAS
Year: 2018
Download: ADS | arXiv


Abstract

The C-Band All-Sky Survey (C-BASS) is an all-sky full-polarization survey at a frequency of 5 GHz, designed to provide complementary data to the all-sky surveys of WMAP and Planck, and future CMB B-mode polarization imaging surveys. The observing frequency has been chosen to provide a signal that is dominated by Galactic synchrotron emission, but suffers little from Faraday rotation, so that the measured polarization directions provide a good template for higher frequency observations, and carry direct information about the Galactic magnetic field. Telescopes in both northern and southern hemispheres with matched optical performance are used to provide all-sky coverage from a ground-based experiment. A continuous-comparison radiometer and a correlation polarimeter on each telescope provide stable imaging properties such that all angular scales from the instrument resolution of 45 arcmin up to full sky are accurately measured. The northern instrument has completed its survey and the southern instrument has started observing. We expect that C-BASS data will significantly improve the component separation analysis of Planck and other CMB data, and will provide important constraints on the properties of anomalous Galactic dust and the Galactic magnetic field.

Sparse estimation of model-based diffuse thermal dust emission

 

Authors: M.O. Irfan, J.Bobin 
Journal: MNRAS
Year: 2017
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Abstract

Component separation for the Planck HFI data is primarily concerned with the estimation of thermal dust emission, which requires the separation of thermal dust from the cosmic infrared background (CIB). For that purpose, current estimation methods rely on filtering techniques to decouple thermal dust emission from CIB anisotropies, which tend to yield a smooth, low- resolution, estimation of the dust emission. In this paper we present a new parameter estimation method, premise: Parameter Recovery Exploiting Model Informed Sparse Estimates. This method exploits the sparse nature of thermal dust emission to calculate all-sky maps of thermal dust temperature, spectral index and optical depth at 353 GHz. premise is evaluated and validated on full-sky simulated data. We find the percentage difference between the premise results and the true values to be 2.8, 5.7 and 7.2 per cent at the 1 sigma level across the full sky for thermal dust temperature, spectral index and optical depth at 353 GHz, respectively. Comparison between premise and a GNILC-like method over selected regions of our sky simulation reveals that both methods perform comparably within high signal-to-noise regions. However outside of the Galactic plane premise is seen to outperform the GNILC-like method with increasing success as the signal-to-noise ratio worsens.

The C-Band All Sky Survey: Separation of Diffuse Galactic Emissions at 5 GHz

 

Authors: M.O. Irfan, C. Dickinson, R.D. Davies, et al.    
Journal: MNRAS
Year: 2015
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Abstract

We present an analysis of the diffuse emission at 5 GHz in the first quadrant of the Galactic plane using two months of preliminary intensity data taken with the C-Band All Sky Survey (C-BASS) northern instrument at the Owens Valley Radio Observatory, California. Combining C-BASS maps with ancillary data to make temperature-temperature plots we find synchrotron spectral indices of β=−2.65±0.05 between 0.408 GHz and 5 GHz and β=−2.72±0.09 between 1.420 GHz and 5 GHz for −10∘<|b|<−4∘, 20∘

The C-Band All-Sky Survey (C-BASS): design and implementation of the northern receiver

 

Authors:

O. G. King,  Michael E. Jones,  E. J. Blackhurst, et al.    

Journal: MNRAS
Year: 2014
Download: ADS | arXiv


Abstract

The C-Band All-Sky Survey (C-BASS) is a project to map the full sky in total intensity and linear polarization at 5 GHz. The northern component of the survey uses a broadband single-frequency analogue receiver fitted to a 6.1-m telescope at the Owens Valley Radio Observatory in California, USA. The receiver architecture combines a continuous-comparison radiometer and a correlation polarimeter in a single receiver for stable simultaneous measurement of both total intensity and linear polarization, using custom-designed analogue receiver components. The continuous-comparison radiometer measures the temperature difference between the sky and temperature-stabilized cold electrical reference loads. A cryogenic front-end is used to minimize receiver noise, with a system temperature of ≈30K in both linear polarization and total intensity. Custom cryogenic notch filters are used to counteract man-made radio frequency interference. The radiometer 1/f noise is dominated by atmospheric fluctuations, while the polarimeter achieves a 1/f noise knee frequency of 10 mHz, similar to the telescope azimuthal scan frequency.