The magic of disc-worlds: non-rotating methanol masers

TL;DR

This paper investigates the dynamics of methanol masers, revealing that many are non-rotating rings likely governed by radial motions such as infall or shocks, challenging gravitational models.

Contribution

It proposes a new interpretation that methanol masers are associated with shock interfaces rather than solely gravitationally driven rotation.

Findings

Most methanol maser rings do not show rotation, but radial motions dominate.

Methanol masers around Cep A show signs of infall.

A model linking masers to shock interfaces at the disk-envelope boundary is discussed.

Abstract

In recent studies of methanol masers, a substantial fraction of the objects show maser components aligned in large-scale elliptical configurations. These can be readily interpreted as rings centred on a high mass star in formation, seen in projection. Remarkably, most of these rings do not show signs of rotation, but rather the radial motions dominate. This must mean that their dynamics are governed by other than gravitational forces. In particular, we have studied the methanol masers around Cep A in detail, where it can be argued that the methanol masers show signs of infall. In this paper we discuss the dynamics of the Cep A methanol maser and sources from the Torun blind survey to argue that at least in a fraction of sources methanol masers could be associated with the shock interface between the large scale accretion, regulated by the magnetic field, and a 1000-AU scale circumstellar disk. We discuss the validity of such a model for the overall population of methanol maser sources.