The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars VI. Insights from Radiative Transfer Modeling

Abstract

We present Markov Chain Monte Carlo radiative transfer modeling of a joint ALMA 345 GHz and spectral energy distribution dataset for a sample of 97 protostellar disks from the VLA and ALMA Nascent Disk and Multiplicity Survey of Orion Protostars. From this modeling, we derive disk and envelope properties for each protostar, allowing us to examine the bulk properties of a population of young protostars. We find that disks are small, with a median dust radius of 29.4 +4.1 −2.7 au and a median dust mass of 5.8 +4.6 −2.7 M ⊕ . We find no statistically significant difference between most properties of Class 0, I, and Flat Spectrum sources with the exception of envelope dust mass and inclination. The distinction between inclination is an indication that the Class 0/I/Flat Spectrum system may be difficult to tie uniquely to the evolutionary state of protostars. When comparing with Class II disk dust masses in Taurus from similar radiative transfer modeling, we further find that the trend of disk dust mass decreasing from Class 0 to Class II disks is no longer present, though it remains unclear whether such a comparison is fair due to differences in star forming region and modeling techniques. Moreover, the disks we model are broadly gravitationally stable. Finally, we compare disk masses and radii with simulations of disk formation and find that magnetohydrodynamical effects may be important for reproducing the observed properties of disks.

Testing a New Model of Embedded Protostellar Disks Against Observation: The Majority of Orion Class 0/I Disks Are Likely Warm, Massive, and Gravitationally Unstable

“…1); this is relatively unlikely for ptotostellar disks. More recently, Sheehan et al (2022) argued that disks in the VANDAM Orion sample are even less massive than the T20 results. However, it would be challenging to quantitatively understand the difference between their results and ours, given the complexity of their model (which has 15 free parameters).…”

“…Another important difference concerns the assumed dust heating mechanism. When translating dust thermal emission to dust mass, most existing studies (e.g., T20; Sheehan & Eisner 2017;Sheehan et al 2022) assume that dust temperature is set mainly by protostellar irradiation, while we assume that the dust temperature is set mainly by the gas in the disk, which is heated internally due to accretion during the main accretion phase.…”

“…This leaves large uncertainties in the result; especially, when the disk is optically thick, this approach can significantly underestimate the disk mass. One can also avoid making these arbitrary assumptions and fit observation with parametrized disk models (often coupled with radiative transfer) with more degrees of freedom (e.g., Sheehan & Eisner 2017;Sheehan et al 2022). A major limitation of this approach, however, is that the model may be underconstrained by data.…”