Self-gravitating disc candidates around massive young stars

TL;DR

This study models candidate massive young star discs to assess their potential for self-gravity, revealing that some observed discs could indeed be marginally unstable and prone to fragmentation, possibly forming companions.

Contribution

The paper introduces semi-analytic models demonstrating that observed discs around massive young stars can be self-gravitating and exhibit weak dust emission due to high optical depth, aligning with observations.

Findings

Some discs are consistent with self-gravitating models.

Self-gravitating discs may undergo fragmentation.

Models match observed disc masses within 1.5 times.

Abstract

There have been several recent detections of candidate Keplerian discs around massive young protostars. Given the relatively large disc-to-star mass ratios in these systems, and their young ages, it is worth investigating their propensity to becoming self-gravitating. To this end, we compute self-consistent, semi-analytic models of putative self-gravitating discs for five candidate disc systems. Our aim is not to fit exactly the observations, but to demonstrate that the expected dust continuum emission from marginally unstable self-gravitating discs can be quite weak, due to high optical depth at the midplane even at millimetre wavelengths. In the best cases, the models produce "observable" disc masses within a factor of <1.5 of those observed, with midplane dust temperatures comparable to measured temperatures from molecular line emission. We find in two cases that a self-gravitating disc model compares well with observations. If these discs are self-gravitating, they satisfy the conditions for disc fragmentation in their outer regions. These systems may hence have as-yet-unresolved low mass stellar companions, and are thus promising targets for future high angular resolution observations.