A New Catalog of Faraday Rotation Measures and Redshifts for Extragalactic Radio Sources

TL;DR

This paper provides a comprehensive catalog of Faraday rotation measures and redshifts for over 4000 extragalactic radio sources, enabling new insights into cosmic magnetic fields and their evolution.

Contribution

It introduces the largest RM and redshift catalog to date, with corrections for Galactic foregrounds, facilitating studies of extragalactic magnetic fields and their properties.

Findings

No significant evolution of residual RM with redshift.

Strong anti-correlation between RRM and fractional polarization.

Evidence for intervening magnetized objects affecting RRM.

Abstract

We present a catalog of Faraday rotation measures (RMs) and redshifts for 4003 extragalactic radio sources detected at 1.4 GHz, derived by identifying optical counterparts and spectroscopic redshifts for linearly polarized radio sources from the NRAO VLA Sky Survey. This catalog is more than an order of magnitude larger than any previous sample of RM vs. redshift, and covers the redshift range 0 < z < 5.3 ; the median redshift of the catalog is z = 0.70, and there are more than 1500 sources at redshifts z > 1. For 3650 of these sources at Galactic latitudes |b| >= 20 degrees, we present a second catalog in which we have corrected for the foreground Faraday rotation of the Milky Way, resulting in an estimate of the residual rotation measure (RRM) that aims to isolate the contribution from extragalactic magnetic fields. We find no significant evolution of RRM with redshift, but observe a strong anti-correlation between RRM and fractional polarization, p, that we argue is the result of beam depolarization from small-scale fluctuations in the foreground magnetic field or electron density. We suggest that the observed variance in RRM and the anti-correlation of RRM with p both require a population of magnetized intervening objects that lie outside the Milky Way but in the foreground to the emitting sources.