RMTable2023 and PolSpectra2023: Standards for Reporting Polarization and Faraday Rotation Measurements of Radio Sources

Abstract

Faraday rotation measures (RMs) have been used for many studies of cosmic magnetism, and in most cases having more RMs is beneficial for those studies. This has lead to the development of RM surveys that have produced large catalogs, as well as meta-catalogs collecting RMs from many different publications. However, it has been difficult to take full advantage of all of these RMs, as the individual catalogs have been published in many different places, and in many different formats. In addition, the polarization spectra used to determine these RMs are rarely published, limiting the ability to reanalyze data as new methods or additional observations become available. We propose a standard convention for RM catalogs, RMTable2023, and a standard for source-integrated polarized spectra of radio sources, PolSpectra2023. These standards are intended to maximize the value and utility of these data for researchers and to make them easier to access. To demonstrate the use of the RMTable2023 standard, we have produced a consolidated catalog of 55,819 RMs collected from 42 published catalogs.

Prototype Faraday Rotation Measure Catalogs from the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM) Pilot Observations

“…The current most complete all-sky RM catalog used to map the Galactic Faraday depth sky by Hutschenreuter et al (2022) is from Van Eck et al (2023) and has an average RM sky density of ∼1.35 RMs per square degree. This low angular resolution limits our ability to map structure on smaller scales.…”

“…Here we compare our prototype RM grids to the current Faraday depth all-sky map from Hutschenreuter et al (2022). The Faraday depth map is constructed from a catalog of RMs compiled by Van Eck et al (2023) from various surveys, the largest of which is from the NVSS Taylor et al (2009) catalog. The Van Eck et al (2023) catalog and has an average density of ∼1.35 RMs per square degree; however, the southern sky is typically more poorly sampled (see Section 1), and the sky density of the catalog in the EC and GL fields is just 0.43 and 0.23 RMs per square degree, respectively.…”

“…The Faraday depth map is constructed from a catalog of RMs compiled by Van Eck et al (2023) from various surveys, the largest of which is from the NVSS Taylor et al (2009) catalog. The Van Eck et al (2023) catalog and has an average density of ∼1.35 RMs per square degree; however, the southern sky is typically more poorly sampled (see Section 1), and the sky density of the catalog in the EC and GL fields is just 0.43 and 0.23 RMs per square degree, respectively. In Figures 16(a) and (b), we plot the RM grids from Section 5.5 and Figure 13 for the EC and GL observations, respectively, overlaid on the Hutschenreuter et al (2022) Faraday depth sky.…”

“…Here we define the table columns for our polarized component catalogs. We follow the RM-Table standard convention for RM catalogs (Van Eck et al 2023) plus provide some additional columns. In Table 5, we provide the units for each column and list the first two rows from the median-filtered GL polarized component catalog.…”

“…Another low-frequency survey in the northern hemisphere, the LOFAR Two-meter Sky Survey (Shimwell et al 2017;O'Sullivan et al 2023), observed from 120 to 168 MHz with an RM sky density of 0.43 RMs per square degree. Most recently, Van Eck et al (2023) consolidated the RM catalogs from 42 publications to produce the largest RM catalog to date, with 55,819 RM measurements across the full sky. Hutschenreuter et al (2022) used this catalog to construct the most complete RM sky map to date.…”