A kinematically detected planet candidate in the transition disk around RXJ1604.3–2130 A

We present ALMA Band 6 dust and gas observations of the transition disk around RXJ1604.3-2130 A, known to feature nearly symmetric shadows in scattered light. We study the ¹²CO line channel maps and moment maps of the line of sight velocity and peak intensity. We fit a Keplerian model of the channel-by-channel emission to study line profile differences, and produce deprojected radial profiles for all velocity components. The ¹²CO emission shows a cavity inwards of ~56 au and within the dust continuum ring at 81 au. The azimuthal brightness variations in the ¹²CO line and dust continuum are broadly aligned with the shadows detected in scattered light observations. We find a strong localized non-Keplerian feature towards the west within the continuum ring (at R=41±10 au and PA=280 ± 2°). A tightly wound spiral is also detected which extends over 300° in azimuth, possibly connected to the localized non-Keplerian feature. Finally, a bending of the iso-velocity contours within the gas cavity indicates a highly perturbed inner region, possibly related to the presence of a misaligned inner disk. While broadly aligned with the scattered light shadows, the localized non-Keplerian feature cannot be solely due to changes in temperature. Instead, we interpret the kinematical feature as tracing a massive companion located at the edge of the dust continuum ring. We speculate that the spiral is caused by buoyancy resonances driven by planet-disk-interactions. However, this potential planet at ∼41 au cannot explain the gas-depleted cavity, the low accretion rate and the misaligned inner disk, suggesting the presence of another companion closer-in.