(a).

For small $\text{g}$, below the critical value $\text{g}^c$ (shown by red symbols in Fig.\[fig:PhD\] (a)), we find the system in a disordered state (D), followed by a flocking phase (F) at $\text{g}>\text{g}^c$, characterized by global polar order induced by the alignment interactions, as expected from the literature of flocking [@VicsekRev]. In simple Vicsek-like models of point-like particles, the flocking state is characterized by the emergence of high density bands close enough to the onset of flocking [@Chate2008; @Solon2015]. Besides this tendency to develop long-range polar order and band patterns due to velocity alignment, in our model, particles aggregate into isotropic clusters as a result of the competition between self-propulsion and short-range repulsions. The interplay between these two interactions, gives rise to a different mechanism for structure formation that we analyze here.

Below the critical value $\text{g}^c$ the system is a non-polar fluid state populated by a distribution of clusters that grow with $\text{Pe}$. This regime is controlled by the physics of ABP (see Fig.\[fig:PhD\] (b)). However, once rotational symmetry has been broken the situation changes radically and new structures, reminiscent to those reported in [@Farrell2012], emerge. At a given finite value of $\text{Pe}$ and for $\text{g}>\text{g}^c$, the model exhibits 