The influence of dust growth on the observational properties of circumplanetary discs

Dust growth is often indirectly inferred observationally in star-forming environments,
theoretically predicted to produce mm-sized particles in circumstellar discs, and also presumably witnessed by the predecessors of the terrestrial meteoritic record. For those reasons it is believed that young gas giants under formation in protoplanetary discs with putative circumplanetary discs (CPDs) surrounding them, such as PDS 70c, should be hosting dusty envelopes of mm-sized particles. We model the spectra of a small set of CPDs, which we obtained from radiation hydrodynamic simulations at varying Rosseland opacities $\kappa_{\rm R}$.
The $\kappa_{\rm R}$ from the hydrodynamic simulations are matched with consistent sets of size-upscaled ISM-like dust populations. Hence, the high $\kappa_{\rm R}$ hydro data nominally corresponds to 10 $\mu$m-sized particles, and the low $\kappa_{\rm R}$-cases corresponds nominally to mm-sized particles. Dust growth to size distributions dominated by millimeter particles generally results in broad, featureless spectra with black-body like slopes in the far-infrared, while size distributions dominated by small dust develop steeper slopes in the far-infrared and maintain some features stemming from individual minerals.
We find that significant dust growth from microns to millimeters can explain the broad features of the PDS 70c data, after scaling up the dust masses from our simulations by $\times$100. Furthermore our results indicate that the spectral range of 30-500 $\mu$m is an ideal hunting ground for broadband features arising from the CPD, but that longer wavelengths observed with ALMA can also be used for massive circumplanetary discs.