  Although active galactic nuclei (AGN) feedback is required in simulations of
galaxies to regulate star formation, further downstream effects on the dark
matter distribution of the halo and stellar kinematics of the central galaxy
can be expected. We combine simulations of galaxies with and without AGN
physics from the Numerical Investigation of a Hundred Astrophysical Objects
(NIHAO) to investigate the effect of AGN on the dark matter profile and central
stellar rotation of the host galaxies. Specifically, we study how the
concentration-halo mass ($c-M$) relation and the stellar spin parameter
($\lambda_R$) are affected by AGN feedback. We find that AGN physics is crucial
to reduce the central density of simulated massive ($\gtrsim 10^{12}$
M$_\odot$) galaxies and bring their concentration to agreement with results
from the Spitzer Photometry & Accurate Rotation Curves (SPARC) sample.
Similarly, AGN feedback has a key role in reproducing the dichotomy between
slow and fast rotators as observed by the ATLAS$^{3\text{D}}$ survey. Without
star formation suppression due to AGN feedback, the number of fast rotators
strongly exceeds the observational constraints. Our study shows that there are
several collateral effects that support the importance of AGN feedback in
galaxy formation, and these effects can be used to constrain its implementation
in numerical simulations.
