  We present a hydrodynamic theory for systems of dipolar active Brownian
particles which, in the regime of weak dipolar coupling, predicts the onset of
motility-induced phase separation (MIPS), consistent with Brownian dynamics
(BD) simulations. The hydrodynamic equations are derived by explicitly
coarse-graining the microscopic Langevin dynamics, thus allowing for a
quantitative comparison of parameters entering the coarse-grained model and
particle-resolved simulations. Performing BD simulations at fixed density, we
find that dipolar interactions tend to hinder MIPS, as first reported in [Liao
et al., Soft Matter, 2020, 16, 2208]. Here we demonstrate that the theoretical
approach indeed captures the suppression of MIPS. Moreover, the analysis of the
numerically obtained, angle-dependent correlation functions sheds light into
the underlying microscopic mechanisms leading to the destabilization of the
homogeneous phase.
