Hot high-mass accretion disk candidates

TL;DR

This study investigates high-mass accretion disk candidates using high-resolution NH3 observations, revealing signatures of rotation and infall but no clear Keplerian disks, suggesting larger envelopes feed smaller disks.

Contribution

First high-resolution NH3 study of high-mass accretion candidates showing detailed kinematic signatures and challenging the presence of large Keplerian disks.

Findings

Most sources show rotation and infall signatures.

No clear Keplerian disks detected at ~1000AU resolution.

Large-scale structures are spherical with clumpy sub-structures.

Abstract

To better understand the physical properties of accretion disks in high-mass star formation, we present a study of a 12 high-mass accretion disk candidates observed at high spatial resolution with the Australia Telescope Compact Array (ATCA) in the NH3 (4,4) and (5,5) lines. Almost all sources were detected in NH3, directly associated with CH3OH Class II maser emission. From the remaining eleven sources, six show clear signatures of rotation and/or infall motions. These signatures vary from velocity gradients perpendicular to the outflows, to infall signatures in absorption against ultracompact HII regions, to more spherical infall signatures in emission. Although our spatial resolution is ~1000AU, we do not find clear Keplerian signatures in any of the sources. Furthermore, we also do not find flattened structures. In contrast to this, in several of the sources with rotational signatures, the spatial structure is approximately spherical with sizes exceeding 10^4 AU, showing considerable clumpy sub-structure at even smaller scales. This implies that on average typical Keplerian accretion disks -- if they exist as expected -- should be confined to regions usually smaller than 1000AU. It is likely that these disks are fed by the larger-scale rotating envelope structure we observe here. Furthermore, we do detect 1.25cm continuum emission in most fields of view.