Diffuse Galactic thermal dust emission: modified black-body parameter maps

Diffuse Galactic thermal dust emission: modified black-body parameter maps


Diffuse emissions are ubiquitous within our Galaxy. They probe star-forming regions, the chemical composition of the Galaxy and the Galactic magnetic field. Conversely, they also obscure cosmological measurements such as the cosmic microwave background and the epoch of reionisation signal. Detailed characterisation of these emissions is of interest to both cosmologists and astrophysicists. In early 2019 CosmoStat released our contribution to the investigation of thermal dust emission in the form of modified black-body temperature, spectral index and optical depth maps (to be found here). These intensity maps are presented at Nside 2048, FWHM 5 arcmin and were made from Planck (data release 2) HFI and IRAS data.

Reference 1: M. Irfan, J. Bobin, M-A. Miville-Deschenes and I. Grenier, "Determining thermal dust emission from Planck HFI data using a sparse parametric technique ", A&A, 623, 03/2019.

 

Determining thermal dust emission from Planck HFI data using a sparse, parametric technique

 

Authors: M.O. Irfan, J.Bobin, M-A.Miville-Deschenes, I.Grenier 
Journal: A&A
Year: 2018
Download: ADS | arXiv


Abstract

Context: The Planck data releases have provided the community with sub-millimetre and radio observations of the full-sky at unprecedented resolutions. We make use of the Planck 353, 545 and 857 GHz maps alongside the IRAS 3000 GHz map. These maps contain information on the cosmic microwave background (CMB), cosmic infrared background (CIB), extragalactic point sources and diffuse thermal dust emission. Aims: We aim to determine the modified black body (MBB) model parameters of thermal dust emission in total intensity and produce all sky maps of pure thermal dust, having separated this Galactic component from the CMB and CIB. Methods: This separation is completed using a new, sparsity-based, parametric method which we refer to as premise. The method comprises of three main stages: 1) filtering of the raw data to reduce the effect of the CIB on the MBB fit. 2) fitting an MBB model to the filtered data across super-pixels of various sizes determined by the algorithm itself and 3) refining these super-pixel estimates into full resolution maps of the MBB parameters. Results: We present our maps of MBB temperature, spectral index and optical depth at 5 arcmin resolution and compare our estimates to those of GNILC as well as the two-step MBB fit presented by the Planck collaboration in 2013. Conclusions: By exploiting sparsity we avoid the need for smoothing, enabling us to produce the first full resolution MBB parameter maps from intensity measurements of thermal dust emission.We consider the premise parameter estimates to be competitive with the existing state-of-the-art solutions, outperforming these methods within low signal-to-noise regions as we account for the CIB without removing thermal dust emission through over-smoothing.

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
Download: ADS | arXiv


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
Download: ADS | arXiv


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.