Polarization fraction of Planck Galactic cold clumps and forecasts for the Simons Observatory

We measure the mean-squared polarization fraction of a sample of 6282 Galactic cold clumps at 353 GHz, consisting of Planck Galactic cold clump (PGCC) catalogue category 1 objects (flux densities measured with signal-to-noise ratio (S/N) >4). At 353 GHz we find the mean-squared polarization fraction, which we define as the mean-squared polarization divided by the mean-squared intensity, to be [4.79 ± 0.44] × 10−4 equation to an 11 σ detection of polarization. We test if the polarization fraction depends on the clumps’ physical properties, including flux density, luminosity, Galactic latitude and physical distance. We see a trend towards increasing polarization fraction with increasing Galactic latitude, but find no evidence that polarization depends on the other tested properties. The Simons Observatory, with angular resolution of order 1′ and noise levels between 22 and 54 μK−arcmin at high frequencies, will substantially enhance our ability to determine the magnetic field structure in Galactic cold clumps. At ≥5 σ significance, we predict the Simons Observatory will detect at least ∼12,000 cold clumps in intensity and ∼430 cold clumps in polarization. This number of polarization detections would represent a two orders of magnitude increase over the current planck results. We also release software that can be used to mask these Galactic cold clumps in other analyses.