Extragalactic Zeeman Detections in OH Megamasers

TL;DR

This study detects Zeeman splitting in OH megamasers across five luminous infrared galaxies, revealing magnetic field strengths comparable to those in the Milky Way and other galaxy phases, offering insights into galactic magnetic environments.

Contribution

First measurement of Zeeman splitting in OH megamasers in multiple (U)LIRGs, demonstrating magnetic fields similar to Galactic values and establishing a new method for studying distant galaxy astrophysics.

Findings

Magnetic fields in (U)LIRGs are similar to Galactic OH masers (~0.5-18 mG).

Magnetic field strengths inferred from Zeeman splitting match those from synchrotron observations.

Zeeman detections in five out of eight targeted galaxies.

Abstract

We have measured the Zeeman splitting of OH megamaser emission at 1667 MHz from five (ultra)luminous infrared galaxies ([U]LIRGs) using the 305 m Arecibo telescope and the 100 m Green Bank Telescope. Five of eight targeted galaxies show significant Zeeman-splitting detections, with 14 individual masing components detected and line-of-sight magnetic field strengths ranging from ~0.5-18 mG. The detected field strengths are similar to those measured in Galactic OH masers, suggesting that the local process of massive star formation occurs under similar conditions in (U)LIRGs and the Galaxy, in spite of the vastly different large-scale environments. Our measured field strengths are also similar to magnetic field strengths in (U)LIRGs inferred from synchrotron observations, implying that milligauss magnetic fields likely pervade most phases of the interstellar medium in (U)LIRGs. These results provide a promising new tool for probing the astrophysics of distant galaxies.