The Galactic Faraday rotation sky 2020

Abstract

Aims. This work provides an update to existing reconstructions of the Galactic Faraday rotation sky by processing almost all Faraday rotation data sets available at the end of the year 2020. Observations of extra-Galactic sources in recent years have further illuminated the previously underconstrained southern celestial sky, as well as parts of the inner disc of the Milky Way, along with other regions. This has culminated in an all-sky data set of 55 190 data points, thereby comprising a significant expansion on the 41 330 used in previous works. At the same time, this novelty makes an updated separation of the Galactic component a promising enterprise. The increased source density allows us to present our results in a resolution of about 1.3 × 10−2 deg2 (46.8 arcmin2), which is a twofold increase compared to previous works. Methods. As for previous Faraday rotation sky reconstructions, this work is based on information field theory, namely, a Bayesian inference scheme for field-like quantities that handles noisy and incomplete data. Results. In contrast to previous reconstructions, we find a significantly thinner and pronounced Galactic disc with small-scale structures exceeding values of several thousand rad m−2. The improvements can mainly be attributed to the new catalog of Faraday data, but are also supported by advances in correlation structure modeling within numerical information field theory. We also provide a detailed discussion on the statistical properties of the Faraday rotation sky and we investigate correlations with other data sets.

Evolution of Primordial Magnetic Fields during Large-scale Structure Formation

“…As the extragalactic polarized emission travels through the magnetized medium between source and observer, there are various contributions along the LOS that add up to the total observed RM. One relevant contribution comes from the Milky Way (see Hutschenreuter et al 2021), but there have been recent efforts in constraining the extragalactic contribution alone (e.g., Schnitzeler 2010;Oppermann et al 2015;Vernstrom et al 2019;O'Sullivan et al 2020). These recent RM observations have constrained the extragalactic RM variance to 5-10 rad m −2 at 1.4 GHz.…”

“…In Figure 9 we show the RM maps of the simulated cosmic web at z = 0.02 for different primordial seeding cases. Note that we did not include the Galactic contribution (Hutschenreuter et al 2021). These maps have been obtained by integrating Equation (5) along the x-axis.…”

CS-ROMER: A novel compressed sensing framework for Faraday depth reconstruction

“…To correct for foreground Galactic rotation, cs-romer provides an option to read the HEALPix image model from Hutschenreuter et al (2022) and use a bilinear interpolation of those data to calculate the mean and standard deviation of the Galactic RM for each line of sight. We denote the interpolated mean image as 𝜙 GAL and the de-rotation of this value can be applied directly as a shift in 𝜆 2 space.…”

“…The mean RM of the Galactic contribution for the Abell 1314 field is 𝜙 GAL = −15 ± 6 rad/m 2 (Hutschenreuter et al 2022). Since this is systematically different from zero, we choose to subtract it from the JVLA measurements.…”

“…Since this is systematically different from zero, we choose to subtract it from the JVLA measurements. This is performed using the cs-romer framework, as described in Section 4.2, by querying the Galactic foreground RM mean and standard deviation maps provided by Hutschenreuter et al (2022). These foreground maps are significantly lower resolution than the JVLA data, and cover the A1314 field using ∼13 pixels.…”