Revealing the dynamics of Class 0 protostellar discs with ALMA

TL;DR

This study uses synthetic ALMA observations to explore the detectability and dynamics of Class 0 protostellar discs, demonstrating that high-resolution, optimal conditions enable early detection and mass estimation of these discs.

Contribution

The paper introduces a new method for accurately determining protostellar masses from ALMA data and assesses the observational conditions needed to detect Keplerian discs at various inclinations and distances.

Findings

ALMA can detect early-stage protostellar discs under optimal conditions.

Keplerian rotation signatures are recognizable in edge-on discs.

Discs can be detected up to kpc distances with sufficient resolution and observing time.

Abstract

We present synthetic ALMA observations of Keplerian, protostellar discs in the Class 0 stage studying the emission of molecular tracers like $^{13}$CO, C$^{18}$O, HCO$^+$, H$^{13}$CO$^+$, N$_2$H$^+$, and H$_2$CO. We model the emission of discs around low- and intermediate-mass protostars. We show that under optimal observing conditions ALMA is able to detect the discs already in the earliest stage of protostellar evolution, although the emission is often concentrated to the innermost 50 AU. Therefore, a resolution of a few 0.1" might be too low to detect Keplerian discs around Class 0 objects. We also demonstrate that under optimal conditions for edge-on discs Keplerian rotation signatures are recognisable, from which protostellar masses can be inferred. For this we here introduce a new approach, which allows us to determine protostellar masses with higher fidelity than before. Furthermore, we show that it is possible to reveal Keplerian rotation even for strongly inclined discs and that ALMA should be able to detect possible signs of fragmentation in face-on discs. In order to give some guidance for future ALMA observations, we investigate the influence of varying observing conditions and source distances. We show that it is possible to probe Keplerian rotation in inclined discs with an observing time of 2 h and a resolution of 0.1", even in the case of moderate weather conditions. Furthermore, we demonstrate that under optimal conditions, Keplerian discs around intermediate-mass protostars should be detectable up to kpc-distances.