arXiv subjects

Luke Jew

Publications and source records attributed to Luke Jew.

3 recordsLinked to original sources

arXiv2019

The C-Band All-Sky Survey (C-BASS): Total intensity point-source detection over the northern sky

We present a point-source detection algorithm that employs the second order Spherical Mexican Hat wavelet filter (SMHW2), and use it on C-BASS northern intensity data to produce a catalogue of point-sources. This catalogue allows us to cross-check the C-BASS flux-density scale against existing source surveys, and provides the basis for a source mask which will be used in subsequent C-BASS and cosmic microwave background (CMB) analyses. The SMHW2 allows us to filter the entire sky at once, avoiding complications from edge effects arising when filtering small sky patches. The algorithm is validated against a set of Monte Carlo simulations, consisting of diffuse emission, instrumental noise, and various point-source populations. The simulated source populations are successfully recovered. The SMHW2 detection algorithm is used to produce a $4.76\,\mathrm{GHz}$ northern sky source catalogue in total intensity, containing 1784 sources and covering declinations $\delta\geq-10^{\circ}$. The C-BASS catalogue is matched with the Green Bank 6\,cm (GB6) and Parkes-MIT-NRAO (PMN) catalogues over their areas of common sky coverage. From this we estimate the $90$ per cent completeness level to be approximately $610\,\mathrm{mJy}$, with a corresponding reliability of $98$ per cent, when masking the brightest $30$ per cent of the diffuse emission in the C-BASS northern sky map. We find the C-BASS and GB6 flux-density scales to be consistent with one another to within approximately $4$ per cent.

astro-ph.CO↗

arXiv2019

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

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.

astro-ph.CO↗

arXiv2019

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

The cosmic microwave background $B$-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 CBASS 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.

astro-ph.CO↗