amount of order in our system by the global polarization $$P=\left\| \frac{1}{N}\sum_i^N \mathbf{n}_i\right\| \, .
\label{op}$$ as typically defined in the context of Vicsek-like models. In Fig.\[fig:Zchi\] (a) we show the behavior of $P$ as a function of $\text{g}$, for several $\text{Pe}$ and averaged over 10-100 independent configurations. As it is commonly done in the study of equilibrium phase transitions, we analyze the susceptibility of the order parameter $P$ defined as $$\chi= N \left( \langle P^2 \rangle - \langle P\rangle^2\right) \, ,$$ where $\langle \cdot \rangle$ represents an average over independent realizations. As shown in Fig. \[fig:Zchi\] (b), $\chi$ is peaked at a value close to the onset of flocking expected from the polarization data. The location of the flocking transition is weakly dependent on $\text{Pe}$, in agreement with continuum hydrodynamic theories [@Farrell2012; @CAP]. The presence of this peak allows us to locate the transition point: we identify the flocking transition (represented by red symbol in the phase diagram Fig. \[fig:PhD\] (a)) with the maximum of $\chi$. Our data shows that the location of the flocking transition is, up to numerical accuracy, independent of the particle’s persistence for $\text{Pe}>1$ and around $\text{g}^c=0.21 \pm 0.02$. Nonetheless, from Fig. \[fig:Zchi\], we notice 