Observations of strong gravitational lensing , stellar kinematics , and larger-scale tracers enable accurate measures of the distribution of dark matter ( DM ) and baryons in massive early-type galaxies ( ETGs ) .
While such techniques have been applied to galaxy-scale and cluster-scale lenses , the paucity of intermediate-mass systems with high-quality data has precluded a uniform analysis of mass-dependent trends .
With the aim of bridging this gap , we present new observations and analyses of 10 group-scale lenses at \langle z \rangle = 0.36 characterized by Einstein radii \theta _ { Ein } = 2 \farcs 5 - 5 \farcs 1 and a mean halo mass of M _ { 200 } = 10 ^ { 14.0 } \textrm { M } _ { \sun } .
We measure a mean concentration c _ { 200 } = 5.0 \pm 0.8 consistent with unmodified cold dark matter halos .
By combining our data with other lens samples , we analyze the mass structure of ETGs in 10 ^ { 13 } \textrm { M } _ { \sun } -10 ^ { 15 } \textrm { M } _ { \sun } halos using homogeneous techniques .
We show that the slope of the total density profile \gamma _ { tot } within the effective radius depends on the stellar surface density , as demonstrated previously , but also on the halo mass .
We analyze these trends using halo occupation models and resolved stellar kinematics with the goal of testing the universality of the DM profile .
Whereas the central galaxies of clusters require a shallow inner DM density profile , group-scale lenses are consistent with a Navarro–Frenk–White profile or one that is slightly contracted .
The largest uncertainties arise from the sample size and likely radial gradients in stellar populations .
We conclude that the net effect of baryons on the DM distribution may not be universal , but more likely varies with halo mass due to underlying trends in star formation efficiency and assembly history .