Source Finding in Linear Polarization for LOFAR, and SKA Predecessor Surveys, using Faraday Moments

Abstract

The optimal source-finding strategy for linear polarization data is an unsolved problem, with many inhibitive factors imposed by the technically-challenging nature of polarization observations. Such an algorithm is essential for Square Kilometre Array (SKA) pathfinder surveys, such as the Multifrequency Snapshot Sky Survey (MSSS) with the LOw Frequency ARray (LOFAR), as data volumes are significant enough to prohibit manual inspection. We present a new strategy of `Faraday Moments' for source-finding in linear polarization with LOFAR, using the moments of the frequency-dependent full-Stokes data (i.e. the mean, standard deviation, skewness, and excess kurtosis). Through simulations of the sky, we find that moments can identify polarized sources with a high completeness: 98.5% at a signal-to-noise of 5. While the method has low reliability, Rotation Measure (RM) Synthesis can be applied per candidate source to filter out instrumental and spurious detections. This combined strategy will result in a complete and reliable catalogue of polarized sources that includes the full sensitivity of the observational bandwidth. We find that the technique can reduce the number of pixels on which RM Synthesis needs to be performed by a factor of $\approx 1\times 10^5$ for source distributions anticipated with modern radio telescopes. Through tests on LOFAR data, we find that the technique works effectively in the presence of diffuse emission. Extensions of this method are directly applicable to other upcoming radio surveys such as the POlarization Sky Survey of the Universe's Magnetism (POSSUM) with the Australia Square Kilometre Array Pathfinder (ASKAP), and the SKA itself.

Accepted for publication in MNRAS

References in corpus (15)

• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey I: A low-frequency extragalactic catalogue
• Science With The Australian Square Kilometre Array Pathfinder
• Estimating extragalactic Faraday rotation
• Calibrating High-Precision Faraday Rotation Measurements for LOFAR and the Next Generation of Low-Frequency Radio Telescopes
• LOFAR/H-ATLAS: A deep low-frequency survey of the Herschel-ATLAS North Galactic Pole field
• The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR
• Faraday tomography of the local interstellar medium with LOFAR: Galactic foregrounds towards IC342
• Initial LOFAR observations of Epoch of Reionization windows: II. Diffuse polarized emission in the ELAIS-N1 field
• Comparison of algorithms for determination of rotation measure and Faraday structure I. 1100 - 1400 MHz
• Subarcsecond international LOFAR radio images of the M82 nucleus at 118 MHz and 154 MHz
• The distribution of polarized radio sources $>$15$\mu$Jy in GOODS-N
• Degree of Polarization and Source Counts of Faint Radio Sources from Stacking Polarized Intensity
• ATLAS 1.4 GHz Data Release 2 -- II. Properties of the faint polarized sky
• The LOFAR long baseline snapshot calibrator survey
• The Magnetic Field and Polarization Properties of Radio Galaxies in Different Accretion States

Cited by in corpus (2)

• The Galactic Magneto-Ionic Medium Survey: Moments of the Faraday Spectra
• The detection of cluster magnetic fields via radio source depolarisation