Resolving the masers in M82

TL;DR

This paper presents high-resolution EVN observations of OH masers in M82, revealing multiple spatial components and suggesting some masers are due to high-gain maser action, enhancing understanding of their nature.

Contribution

First high-resolution EVN observations resolve multiple components of M82 masers, providing new insights into their spatial structure and emission mechanisms.

Findings

Masers are spatially resolved into multiple components.

Some masers exhibit high-gain maser action.

Masers are associated with background continuum features.

Abstract

Despite first being detected in the 1970s, surprisingly little is known about the OH main line maser population in the nearby starburst galaxy M82. Sometimes referred to as 'kilomasers', they have isotropic luminosities intermediate between Galactic masers and those found in more distant megamasers. Several observations have been carried by this group over the last ten years in an attempt to get a better handle on their nature. High velocity resolution VLA observations in 2006 showed that almost all of the maser spots, distributed across the central arcminute of the galaxy, were apparently coincident with background continuum features, and a handful displayed multiple velocity components. The majority of those with velocity structure are located on a blue-shifted arc in the pv-plane, spatially located on an arc northward of the peculiar source known as B41.95+57.5. Now, new results from high spatial and spectral resolution observations with the EVN have resolved several of these masers into multiple spatial components for the first time. The maser emission is compared with known continuum sources in the galaxy, and we conclude that at least some of the maser emission is from high-gain maser action.