  We study a system of interacting active particles, propelled by colored
noises, characterized by an activity time {\tau}, and confined by a single-well
anharmonic potential. We assume pair-wise repulsive forces among particles,
modelling the steric interactions among microswimmers. This system has been
experimentally studied in the case of a dilute suspension of Janus particles
confined through acoustic traps. We observe that already in the dilute regime -
when inter-particle interactions are negligible - increasing the persistent
time pushes the particles away from the potential minimum, until a saturation
distance is reached. We compute the phase diagram (activity versus interaction
length), showing that the interaction does not suppress this delocalization
phenomenon but induces a liquid- or solid-like structure in the densest
regions. Interestingly a reentrant behavior is observed: a first increase of
{\tau} from small values acts as an effective warming, favouring fluidization;
at higher values, when the delocalization occurs, a further increase of {\tau}
induces freezing inside the densest regions. An approximate analytical scheme
gives fair predictions for the density profiles in the weakly interacting case.
The analysis of non-equilibrium heat fluxes reveals that in the region of
largest particle concentration equilibrium is restored in several aspects.
