Interstellar clouds can act as target material for hadronic cosmic rays; gamma-rays produced through inelastic proton-proton collisions and spatially associated with the clouds can provide a key indicator of efficient particle acceleration.
However, even for PeVatron sources reaching PeV energies, the system of cloud and accelerator must fulfil several conditions in order to produce a detectable gamma-ray flux.
In this contribution, we characterise the necessary properties of both cloud and accelerator.
Using available Supernova Remnant (SNR) and interstellar cloud catalogues, and assuming particle acceleration to PeV energies in a nearby SNR, we produce a ranked shortlist of the most promising target systems, for which a detectable gamma-ray flux is predicted.
We discuss detection prospects for future facilities including CTA, LHAASO and SWGO; and compare our predictions with known gamma-ray sources.
A range of model scenarios are tested, including variation in the diffusion coefficient and particle spectrum, under which the best candidate clouds in our shortlist are consistently bright.
On average, a detectable gamma-ray flux is more likely for more massive clouds; for systems with lower separation distance between the SNR and cloud; and for slightly older SNRs.