Description
Circumplanetary disks (CPDs) are accretion disks surrounding forming planets and are thought to play an important role in planet and moon formation. However, their small spatial scales and faint emission make them difficult to detect, requiring deep, high-resolution observations.
The exoALMA survey (Teague et al. 2025) provides some of the deepest high-resolution observations of planet-forming disks obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). This study searched the outer regions of 15 exoALMA disks for compact CPD candidates, where contamination from bright central disk emission is reduced.
Azimuthally averaged radial noise profiles were derived using the median absolute deviation of deprojected residual maps. These profiles were used to construct two-dimensional signal-to-noise ratio (SNR) maps and identify robust, beam-sized, high-SNR features. Detection sensitivity was assessed through injection-recovery experiments. Candidate detections were compared with published CO ``kinks,'' observations from other ALMA surveys and bands, including DSHARP, and previously reported planet candidates and disk anomalies.
Three compact features with significances above $3\sigma$ and central peak brightnesses above $5\sigma$ were identified in CQ~Tau and V4046~Sgr. In DM~Tau, an extended residual structure with a peak significance of $9.46\sigma$ was detected at a location not previously reported outside the exoALMA Band~7 data. However, its extent is substantially larger than a single synthesized beam, suggesting that it is unlikely to be a compact CPD and may instead trace a background source.
Combining the detected sources with disk gaps and kinematic signatures enables the properties of potential CPDs, including their size, mass, viscosity, and accretion rate, to be constrained through forward modelling such as that of Zhu et al. (2018). These constraints provide quantitative CPD upper limits and guide targeted follow-up observations.
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