MeerKAT

Abstract:

The ALMACAL −22 surv e y includes o v er 2700 h of observations of ALMA phase and amplitude calibrators, spanning frequencies from 84 to 950 GHz across bands 3 to 10. In total, 687 out of the 1047 calibrators have redshifts confirmed with spectroscopy and we find an additional 50 featureless blazars. The redshift distribution of the ALMACAL-22 sample peaks at z ≈1 and spans a wide range, from the nuclei of nearby galaxies at z ≪0 . 01 to quasars at z = 3 . 742. 70 new VLT/X-Shooter spectra of these sources co v ering UV to NIR wavelengths are also presented, which will be used in future stacking experiments to search for cold gas in the circumgalactic medium. Infrared magnitudes from WISE indicate that the majority of the sources are consistent with being quasars or blazars. After fitting the radio spectral energy distributions of the calibrators, we find that most ALMA calibrators exhibit peaked spectra or are re-triggered which is surprising given the large number of blazars in the sample. The peak frequencies span three orders of magnitude from 100 MHz to 170 GHz, corresponding to linear sizes ranging from sub-pc to > 10 kpc. In the future, when combined with high-resolution radio imaging, these results will of fer v aluable constraints on the molecular gas content of the CGM, as well as the ages and duty cycles of AGN jets. The e ver-gro wing ALMACAL data set will remain an indispensable resource for studying the various aspects of galaxy formation and evolution.

Abstract:

Measuring the magnetic field of the Milky Way reveals the structure and evolution of the Galaxy. Pulsar rotation measures (RMs) provide a means to probe this Galactic magnetic field (GMF) in three dimensions. We use the largest single-origin data set of pulsar measurements, from the MeerKAT Thousand-Pulsar-Array, to map out GMF components parallel to pulsar lines of sight. We also present these measurements for easy integration into the consolidated RM catalogue, RMTable. Focusing on the Galactic disc, we investigate competing theories of how the GMF relates to the spiral arms, comparing our observational map with five analytic models of magnetic field structure. We also analyse RMs to extragalactic radio sources, to help build-up a three-dimensional picture of the magnetic structure of the Galaxy. In particular, our large number of measurements allows us to investigate differing magnetic field behaviour in the upper and lower halves of the Galactic plane. We find that the GMF is best explained as following the spiral arms in a roughly bisymmetric structure, with antisymmetric parity with respect to the Galactic plane. This picture is complicated by variations in parity on different spiral arms, and the parity change location appears to be shifted by a distance of 0.15 kpc perpendicular to the Galactic plane. This indicates a complex relationship between the large-scale distributions of matter and magnetic fields in our Galaxy. Future pulsar discoveries will help reveal the origins of this relationship with greater precision, as well as probing the locations of local magnetic field inhomogenities.