# Observing the gas component of circumplanetary disks around wide-orbit planet-mass companions in the (sub)mm regime

## TL;DR

This study models the gas component of circumplanetary disks around wide-orbit planet-mass companions to assess their detectability with (sub)mm telescopes like ALMA, providing insights into disk properties and companion masses.

## Contribution

It introduces a detailed modeling approach to predict gas observability in circumplanetary disks, guiding future detection strategies and constraining formation theories.

## Key findings

- Disks with ~10 au radius are detectable in CO lines at 150 pc with ALMA in 6 hours.
- Detection of gas disks can help estimate the mass of the companion via kinematic signatures.
- Non-detections can still constrain disk size and gas mass, informing formation models.

## Abstract

Several detections of wide-orbit planet-mass/sub-stellar companions around young solar-like stars were reported in the last decade. The origin of those possible planets is still unclear but accretion tracers and VLT/SPHERE observations indicate that they are surrounded by circumplanetary material or even a circumplanetary disk. We want to investigate if the gas component of disks around wide-orbit companions is detectable with current and future (sub)mm telescopes and what constraints such gas observations can provide on the nature of the circumplanetary material and on the mass of the companion. We applied the radiation thermo-chemical disk code ProDiMo to model the dust and gas component of passive circumplanetary disks and produced realistic synthetic observables. We considered different companion properties, disk parameters and radiative environments and compared the resulting synthetic observables to telescope sensitivities and to existing dust observations. The main criterion for a successful detection is the size of the circumplanetary disk. At a distance of about 150 pc, a circumplanetary disk with an outer radius of about 10 au is detectable with ALMA in about 6 hours in optically thick CO lines. Other aspects such as the companion's luminosity, disk inclination and background radiation fields are also relevant and should be considered to optimize the observing strategy for detection experiments. For most of the known wide-orbit planet-mass companions, their maximum theoretical disk size of one third of the Hill radius would be sufficient to allow detection of CO lines. It is therefore feasible to detect their gas disks and constrain the mass of the companion through the kinematic signature. Even in the case of non-detections such observations will provide stringent constraints on disk size and gas mass, information crucial for formation theories.