Publications by Luke Jew


The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region

Monthly Notices of the Royal Astronomical Society Oxford University Press 485 (2019) 2844–2860-

C Dickinson, A Barr, HC Chiang, C Copley, RDP Grumitt, HM Heilgendorff, LRP Jew, JL Jonas, ME Jones, JP Leahy, J Leech, EM Leitch, SJC Muchovej, TJ Pearson, MW Peel, ACS Readhead, J Sievers, MA Stevenson, A Taylor

The C-Band All-Sky Survey (C-BASS) is a high sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a total intensity map of the North Celestial Pole (NCP) region of sky, above declination >+80°, which is limited by source confusion at a level of ≈0.6 mK rms. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ∼20–40 GHz. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (⁠<10 per cent⁠) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of 9.93 ± 0.35 and 9.52±0.34 K per unit τ353 when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes 55±2μK rms at 22.8 GHz and accounts for ≈60 per cent of the total foreground emission. Our results show that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies ≳5 GHz; the best-fitting synchrotron temperature spectral index is β = −2.91 ± 0.04 from 4.7 to 22.8 GHz and β = −2.85 ± 0.14 from 22.8 to 44.1 GHz. Free–free emission is weak, contributing ≈7μK rms (⁠≈7 per cent⁠) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains.


The C-Band All-Sky Survey (C-BASS): Simulated parametric fitting in single pixels in total intensity and polarization

Monthly Notices of the Royal Astronomical Society Oxford University Press 490 (2019) 2958–2975-

L Jew, AC Taylor, M Jones, A Barr, HC Chiang, C Dickinson, RDP Grumitt, HM Heilgendorff, J Hill-Valler, JL Jonas, JP Leahy, J Leech, TJ Pearson, MW Peel, ACS Readhead, J Sievers

The cosmic microwave background (CMB) B-mode signal is potentially weaker than the diffuse Galactic foregrounds over most of the sky at any frequency. A common method of separating the CMB from these foregrounds is via pixel-based parametric-model fitting. There are not currently enough all-sky maps to fit anything more than the most simple models of the sky. By simulating the emission in seven representative pixels, we demonstrate that the inclusion of a 5 GHz data point allows for more complex models of low-frequency foregrounds to be fitted than at present. It is shown that the inclusion of the C-BASS data will significantly reduce the uncertainties in a number of key parameters in the modelling of both the galactic foregrounds and the CMB. The extra data allow estimates of the synchrotron spectral index to be constrained much more strongly than is presently possible, with corresponding improvements in the accuracy of the recovery of the CMB amplitude. However, we show that to place good limits on models of the synchrotron spectral curvature will require additional low-frequency data.


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

Monthly Notices of the Royal Astronomical Society Oxford University Press 480 (2018) 3224–3242-

M Jones, A Taylor, M Aich, CJ Copley, HC Chiang, RJ Davis, C Dickinson, R Grumitt, Y Hafez, HM Heilgendorff, CM Holler, MO Irfan, L Jew, J John, J Jonas, OG King, JP Leahy, J Leech, EM Leitch, SJC Muchovej, TJ Pearson, MW Peel, ACS Readhead, J Sievers, MA Stevenson

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.


The state-of-play of Anomalous Microwave Emission (AME) research

New Astronomy Reviews Elsevier (2018)

BT Draine, R Génova-Santos, Harper, B Hensley, JR Hill-Valler, T Hoang, FP Israel, L Jew, A Lazarian, JP Leahy, J Leech, CH López-Carabello, I McDonald, EJ Murphy, T Onaka, R Paladini, MW Peel, Y Perrott, F Poidevin, ACS Readhead, J-A Rubiño-Martín, AC Taylor, CT Tibbs, M Todorovic, M Vidal

Anomalous Microwave Emission (AME) is a component of diffuse Galactic radiation observed at frequencies in the range ≈10–60 GHz. AME was first detected in 1996 and recognised as an additional component of emission in 1997. Since then, AME has been observed by a range of experiments and in a variety of environments. AME is spatially correlated with far-IR thermal dust emission but cannot be explained by synchrotron or free–free emission mechanisms, and is far in excess of the emission contributed by thermal dust emission with the powerlaw opacity consistent with the observed emission at sub-mm wavelengths. Polarization observations have shown that AME is very weakly polarized ( ≲ 1 %). The most natural explanation for AME is rotational emission from ultra-small dust grains (“spinning dust”), first postulated in 1957. Magnetic dipole radiation from thermal fluctuations in the magnetization of magnetic grain materials may also be contributing to the AME, particularly at higher frequencies ( ≳ 50 GHz). AME is also an important foreground for Cosmic Microwave Background analyses. This paper presents a review and the current state-of-play in AME research, which was discussed in an AME workshop held at ESTEC, The Netherlands, June 2016.


The spectral index of polarized diffuse Galactic emission between 30 and 44 GHz

ArXiv (0)

L Jew, R Grumitt

We present an estimate of the polarized spectral index between the Planck 30 and 44 GHz surveys in $3.7^\circ$ pixels across the entire sky. We use an objective reference prior that maximises the impact of the data on the posterior and multiply this by a maximum entropy prior that includes information from observations in total intensity by assuming a polarization fraction. Our parametrization of the problem allows the reference prior to be easily determined and also provides a natural method of including prior information. The spectral index map is consistent with those found by others between surveys at similar frequencies. Across the entire sky we find an average temperature spectral index of $-2.99\pm0.03(\pm1.12)$ where the first error term is the statistical uncertainty on the mean and the second error term (in parentheses) is the extra intrinsic scatter in the data. We use a clustering algorithm to identify pixels with actual detections of the spectral index. The average spectral index in these pixels is $-3.12\pm0.03(\pm0.64)$ and then when also excluding pixels within $10^\circ$ of the Galactic plane we find $-2.92(\pm0.03)$. We find a statistically significant difference between the average spectral indices in the North and South Fermi bubbles. Only including pixels identified by the clustering algorithm, the average spectral index in the southern bubble is $-3.00\pm0.05(\pm0.35)$, which is similar to the average across the whole sky. In the northern bubble we find a much harder average spectral index of $-2.36\pm0.09(\pm0.63)$. Therefore, if the bubbles are features in microwave polarization they are not symmetric about the Galactic plane.