The SLUGGS Survey: A comparison of total-mass profiles of early-type
  galaxies from observations and cosmological simulations, to $\sim$4 effective
  radii
  We apply the Jeans Anisotropic MGE (JAM) dynamical modelling method to SAGES
Legacy Unifying Globulars and GalaxieS (SLUGGS) survey data of early-type
galaxies in the stellar mass range $10^{10}<M_*/{\rm M}_{\odot}<10^{11.6}$ that
cover a large radial range of $0.1-4.0$ effective radii. We combine SLUGGS and
ATLAS$^{\rm 3D}$ datasets to model the total-mass profiles of a sample of 21
fast-rotator galaxies, utilising a hyperparameter method to combine the two
independent datasets. The total-mass density profile slope values derived for
these galaxies are consistent with those measured in the inner regions of
galaxies by other studies. Furthermore, the total-mass density slopes
($\gamma_{\rm tot}$) appear to be universal over this broad stellar mass range,
with an average value of $\gamma_{\rm tot}=-2.12\,\pm\,0.05$, i.e. slightly
steeper than isothermal. We compare our results to model galaxies from the
Magneticum and EAGLE cosmological hydrodynamic simulations, in order to probe
the mechanisms that are responsible for varying total-mass density profile
slopes. The simulated-galaxy slopes are shallower than the observed values by
$\sim0.1-0.3$, indicating that the physical processes shaping the mass
distributions of galaxies in cosmological simulations are still incomplete. For
galaxies with $M_*>10^{10.7}{\rm M}_{\odot}$ in the Magneticum simulations, we
identify a significant anticorrelation between total-mass density profile
slopes and the fraction of stellar mass formed ex situ (i.e. accreted), whereas
this anticorrelation is weaker for lower stellar masses, implying that the
measured total mass density slopes for low-mass galaxies are less likely to be
determined by merger activity.
