2025PASJ...77..572S

This study focuses on Class I, flat spectrum (FS), and Class II disks in the Ophiuchus molecular cloud, a nearby active star-forming region with numerous young stellar objects, to unveil signs of substructure formation in these disks. We employ two-dimensional super-resolution imaging based on sparse modeling for ALMA archival Band 6 continuum data, achieving images with spatial resolutions comparable to a few au ($0{_{.}^{\prime\prime}}02$-$0{_{.}^{\prime\prime}}2$) for 78 dust disks, all of which are spatially resolved. In our sample, we confirm that approximately 30%-40% of the disks exhibit substructures, and we identify new substructures in 15 disks (four Class I, seven Class FS, and four Class II objects). Compared to the eDisk sample in terms of bolometric temperature, $T_{\rm bol}$, our targets are in a later accretion phase. By combining our targets with the eDisk sample, we confirm that substructure detection in available data is restricted to objects where $T_{\rm bol}$ exceeds 200-300 K and the dust disk radius, $R_{\rm dust}$, is larger than $\sim$30 au. Moreover, we find that the distribution of inclination angles for Class II disks has a deficit of high values and is not consistent with being random. Analyzing molecular line emission data around these objects will be crucial to constrain disk evolutionary stages further and understand when and how substructures form.