2015MNRAS.452L..21S

We conduct a detailed lensing, dynamics and stellar population analysis of nine massive lens early-type galaxies (ETGs) from the X-Shooter Lens Survey (XLENS). Combining gravitational lensing constraints from HST imaging with spatially-resolved kinematics and line-indices constraints from Very Large Telescope (VLT) X-Shooter spectra, we infer the low-mass slope and the low cut-off mass of the stellar initial mass function (IMF): x_250=2.37^+0.12_-0.12 and M_low, 250= 0.131^+0.023_-0.026 M_☉, respectively, for a reference point with σ{sstarf} ≡ 250 km/s and Reff ≡ 10 kpc. All the XLENS systems are consistent with an IMF slope steeper than Milky Way-like. We find no significant correlations between IMF slope and any other quantity, except for an anticorrelation between total dynamical mass density and low-mass IMF slope at the 87 percent CL [dx/dlog(ρ) = -0.19^+0.15_-0.15]. This anticorrelation is consistent with the low-redshift lenses found by Smith et al. that have high velocity dispersions and high stellar mass densities but surprisingly shallow IMF slopes.