Formation of dust clumps with sub-Jupiter mass and cold shadowed region in gravitationally unstable disk around Class 0/I protostar in L1527 IRS

Abstract

We have investigated the protostellar disk around a Class 0/I protostar, L1527 IRS, using multi-wavelength observations of the dust continuum emission at $\lambda =0.87$, 2.1, 3.3, and 6.8 mm obtained by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array (VLA). Our observations achieved a spatial resolution of $3-13$ au and revealed an edge-on disk structure with a size of $\sim 80-100$ au. The emission at 0.87 and 2.1 mm is found to be optically thick within a projected disk radius of $r_{\mathrm{proj}}\lesssim 50$ au. The emission at 3.3 and 6.8 mm shows that the power-law index of the dust opacity ($\beta$) is $\beta \sim 1.7$ around $r_{\mathrm{proj}}\sim 50$ au, suggesting that grain growth has not yet begun. The dust temperature ($T_{\mathrm{dust}}$) shows a steep decrease with $T_{\mathrm{dust}}\propto r_{\mathrm{proj}}^{-2}$ outside of the VLA clumps previously identified at $r_{\mathrm{proj}}\sim 20$ au. Furthermore, the disk is gravitationally unstable at $r_{\mathrm{proj}}\sim 20$ au, as indicated by a Toomre {\it Q} parameter value of $Q\lesssim 1.0$. These results suggest that the VLA clumps are formed via gravitational instability, which creates a shadow on the outside of the substructure, resulting in the sudden drop in temperature. The derived dust masses for the VLA clumps are $\gtrsim 0.1$ $M_{\mathrm{J}}$. Thus, we suggest that Class 0/I disks can be massive enough to be gravitationally unstable, which might be the origin of gas-giant planets in a 20 au radius. Furthermore, the protostellar disks can be cold due to shadowing.

23 pages, 18 figures, 1 table. Accepted for publication in ApJ

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• The Molecular Composition of Shadowed Protosolar Disk Midplanes beyond the Water Snowline
• A millimeter-multiwavelength continuum study of VLA 1623 West
• Filling in the Gaps: Can Gravitationally Unstable Discs Form the Seeds of Gas Giant Planets?
• Early Planet Formation in Embedded Disks (eDisk). XI. A high-resolution view toward the BHR 71 Class 0 protostellar wide binary
• Synthetic Observations of the Infalling Rotating Envelope: Links between the Physical Structure and Observational Features