We study the total mass-density profile for a sample of 14 fast-rotator early-type galaxies ( stellar masses 10.2 \lesssim \log M _ { \ast } / M _ { \odot } \lesssim 11.7 ) .
We combine observations from the SLUGGS and ATLAS ^ { 3 D } surveys to map out the stellar kinematics in two-dimensions , out to a median radius for the sample of four half-light radii R _ { e } ( or 10 kpc ) , and a maximum radius of 2.0–6.2 R _ { e } ( or 4–21 kpc ) .
We use axisymmetric dynamical models based on the Jeans equations , which allow for a spatially varying anisotropy , and employ quite general profiles for the dark halos , and in particular do not place any restriction on the profile slope .
This is made possible by the availability of spatially extended two-dimensional kinematics .
We find that our relatively simple models provide a remarkably good description of the observed kinematics .
The resulting total density profiles are well described by a nearly-isothermal power law \rho _ { tot } ( r ) \propto r ^ { - \gamma } from R _ { e } /10 to at least 4 R _ { e } , the largest average deviation being 11 % .
The average logarithmic slope is \langle \gamma \rangle = 2.19 \pm 0.03 with observed rms scatter of just \sigma _ { \gamma } = 0.11 .
This scatter out to large radii , where dark matter dominates , is as small as previously reported by lensing studies around r \approx \hbox { $R _ { e } $ } / 2 , where the stars dominate .
Our bulge-halo conspiracy places much tighter constraints on galaxy formation models .
It illustrates the power of two-dimensional stellar kinematics observations at large radii .
It would now be important to test the generality of our results for different galaxy types and larger samples .