Testing a New Model of Protostellar Disks Against Observation: The
  Majority of Orion Class 0/I Disks Are Likely Warm, Massive, and
  Gravitationally Unstable
  We formulate a parametrized model of protostellar disks and test its ability
to estimate disk properties by fitting dust-continuum observations. The main
physical assumptions of our model are motivated by a recent theoretical study
of protostellar disk formation; these assumptions include that the disk should
be marginally gravitationally unstable, and that the dominant dust heating
mechanism is internal accretion heating instead of external protostellar
irradiation. These assumptions allow our model to reliably estimate the disk
mass even when the observed emission is optically thick and to
self-consistently determine disk (dust) temperature. Using our model to fit
multi-wavelength observations of 156 disks in the VANDAM Orion survey, we find
that the majority (57%) of this sample can be fit well by our model. Moreover,
the observations prefer our fiducial model with marginally unstable Toomre $Q$
compared to models with larger $Q$ values, suggesting that the majority of
disks in our sample are likely gravitationally unstable. Using our model, we
produce new estimates of Orion protostellar disk properties. We find that these
disks are generally warm and massive, with a typical star-to-disk mass ratio
$M_{\rm d}/M_\star = \mathcal O(1)$ in Class 0/I. We also discuss why our
estimates differ from those in previous studies and the implications of our
results on disk evolution and fragmentation.
