Strong-lensing measurement of the total-mass-density profile out to three effective radii for z ∼ 0.5 early-type galaxies

Abstract

ABSTRACT We measure the total-mass-density profiles out to three effective radii for a sample of 63$z$ ∼ 0.5, massive early-type galaxies (ETGs) acting as strong gravitational lenses through a joint analysis of lensing and stellar dynamics. The compilation is selected from three galaxy-scale strong-lens samples, namely the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS), the BELLS for GALaxy-Lyα EmitteR sYstems Survey (BELLS GALLERY), and the Strong Lensing Legacy Survey (SL2S). Utilizing the wide source-redshift coverage (0.8–3.5) provided by these three samples, we build a statistically significant ensemble of massive ETGs for which robust mass measurements can be achieved within a broad range of Einstein radii up to three effective radii. Characterizing the three-dimensional total-mass-density distribution by a power-law profile as ρ ∝ r−γ, we find that the average logarithmic density slope for the entire sample is $\langle \gamma \rangle =2.000_{-0.032}^{+0.033}$ (68 per cent CL) with an intrinsic scatter of $\delta =0.180_{-0.028}^{+0.032}$. Further parametrizing 〈γ〉 as a function of redshift $z$ and the ratio of Einstein radius to effective radius Rein/Reff, we find that the average density distributions of these massive ETGs become steeper at later cosmic times and at larger radii, with magnitudes $\mathrm{d} \langle \gamma \rangle / \mathrm{d}z=-0.309_{-0.160}^{+0.166}$ and $\mathrm{d} \langle \gamma \rangle / \mathrm{d} \log _{10} ({R_{\rm ein}}/{R_{\rm eff}})=0.194_{-0.083}^{+0.092}$.