Early Planet Formation in Embedded Disks (eDisk). VIII. A Small
Protostellar Disk around the Extremely Low-Mass and Young Class 0 Protostar,
IRAS 15398-3359
Protostellar disks are a ubiquitous part of the star formation process and
the future sites of planet formation. As part of the Early Planet Formation in
Embedded Disks (eDisk) large program, we present high-angular resolution dust
continuum (∼40mas) and molecular line (∼150mas) observations of
the Class 0 protostar, IRAS 15398-3359. The dust continuum is small, compact,
and centrally peaked, while more extended dust structures are found in the
outflow directions. We perform a 2D Gaussian fitting to find the deconvolved
size and 2σ radius of the dust disk to be 4.5×2.8au
and 3.8au, respectively. We estimate the gas+dust disk mass
assuming optically thin continuum emission to be 0.6−1.8Mjup,
indicating a very low-mass disk. The CO isotopologues trace components of the
outflows and inner envelope, while SO traces a compact, rotating disk-like
component. Using several rotation curve fittings on the PV diagram of the SO
emission, the lower limits of the protostellar mass and gas disk radius are
0.022M⊙ and 31.2au from our Modified 2 single power-law
fitting. A conservative upper limit of the protostellar mass is inferred to be
0.1M⊙. The protostellar mass-accretion rate and the specific angular
momentum at the protostellar disk edge are found to be between
1.3−6.1×10−6M⊙yr−1 and
1.2−3.8×10−4kms−1pc, respectively, with an age
estimated between 0.4−7.5×104yr. At this young age with no clear
substructures in the disk, planet formation would likely not yet have started.
This study highlights the importance of high-resolution observations and
systematic fitting procedures when deriving dynamical properties of deeply
embedded Class 0 protostars.Comment: 28 pages, 16 figures. Accepted for publication in ApJ as one of the
first-look papers of the eDisk ALMA Large Progra