  We study active run-and-tumble particles with an additional two-state
internal variable characterizing their motile or non-motile state. Motile
particles change irreversibly into non-motile ones upon collision with a
non-motile particle. The system evolves towards an absorbing state where all
particles are non-motile. We initialize the system with one non-motile
particles in a bath of motile ones and study numerically the kinetics of
relaxation to absorbing state and its structure as function of the density of
the initial bath of motile particles and of their tumbling rate. We find a
crossover from fractal aggregates at low density to homogeneous ones at high
density. The persistence of single-particle dynamics as quantified by the
tumbling rate pushes this crossover to higher density and can be used to tune
the porosity of the aggregate. At the lowest density the fractal dimension of
the aggregate approaches that obtained in single-particle diffusion limited
aggregation. Our results could be exploited for the design of structures of
desired porosity. The model is a first step towards the study of the collective
dynamics of active particles that can exchange biological information.
