Dark matter halo properties from galaxy–galaxy lensing★

We present results for a galaxy–galaxy lensing study based on imaging data from the Canada–France–Hawaii Telescope Legacy Survey Wide. From a 12 million object multicolour catalogue for 124 deg2 of photometric data in the u*g′r′i′z′ filters, we compute photometric redshifts (with a scatter of σΔz/(1 + z) = 0.033 and an outlier rate of η = 2.0 per cent for i′ ≤ 22.5) and extract galaxy shapes down to i′ = 24.0. We select a sample of lenses and sources with 0.05 < zd ≤ 1 and 0.05 < zs ≤ 2. We fit three different galaxy halo profiles to the lensing signal, a singular isothermal sphere (SIS), a truncated isothermal sphere (BBS) and a universal density profile (NFW). We derive velocity dispersions by fitting an SIS out to 100 h−1 kpc to the excess surface mass density ΔΣ and perform maximum likelihood analyses out to a maximum scale of 2 h−1 Mpc to obtain halo parameters and scaling relations. We find luminosity scaling relations of σred ∝ L0.24 ± 0.03 for the red lens sample, σblue ∝ L0.23 ± 0.03 for blue lenses and σ ∝ L0.29 ± 0.02 for the combined lens sample with zero-points of |$\sigma ^{*}_{\rm red}=162\pm 2\,{\rm km\ s^{-1}}$|⁠, |$\sigma ^{*}_{\rm blue}=115\pm 3\,{\rm km\ s^{-1}}$| and σ* = 135 ± 2 km s−1 at a chosen reference luminosity |$L^{*}_{r^{\prime}}=1.6 \times 10^{10}\ h^{-2}\ L_{r^{\prime},\odot}$|⁠. The steeper slope for the combined sample is due to the different zero-points of the blue and red lenses and the fact that blue lenses dominate at low luminosities and red lenses at high luminosities. The mean effective redshifts for the lens samples are 〈zred〉 = 0.28 for red lenses, 〈zblue〉 = 0.35 for blue lenses and 〈z〉 = 0.34 for the combined lens sample. The BBS maximum likelihood analysis yields for the combined sample a velocity dispersion of |$\sigma ^{*} = 131^{+2}_{-2}$| km s− 1 and a truncation radius of |$s^{*} = 184^{+17}_{+14} \ h^{-1}$| kpc, corresponding to a total mass of |$M^{*}_{\rm {total,BBS}} = 2.32^{+0.28}_{-0.25} \times 10^{12} \ h^{-1} \ {\rm M}_{{\odot }}$| and a mass-to-light (M/L) ratio of |$M^{*}_{\rm total,BBS}/L^{*}=178^{+22}_{-19} \ h \ {\rm M}_{{\odot }}/L_{r^{\prime },{\odot }}$| at |$L^{*}_{r^\prime}$|⁠. At a given luminosity, both velocity dispersion σ and truncation radius s are larger for red galaxies than for blue galaxies. For an NFW profile, we measure at |$L^{*}_{r^\prime}$| a virial radius of |$r^{*}_{200} = 133^{+3}_{-2} \ h^{-1}$| kpc and a concentration parameter of |$c^{*} = 6.4^{+0.9}_{-0.7}$|⁠, implying a virial mass of |$M^{*}_{200} = 7.6^{+0.5}_{-0.3} \times 10^{11} \ h^{-1} \,\mathrm{M}_{{\odot }}$|⁠. At L* for blue galaxies the concentration parameter is slightly higher than for red galaxies and r200 is significantly lower. For the combined sample, if described as a single power law, the M/L ratio scales as |$M_{\rm total, BBS}/L \propto L^{0.12^{+0.10}_{-0.11}}$|⁠, the concentration parameter scales as |$c \propto L^{-0.07^{+0.11}_{-0.11}}$|⁠. Analysing the M/L scaling for red and blue galaxies separately, we find that a broken power law (with a flat slope at high luminosities) provides a more appropriate description for red and possibly also for blue galaxies. We measure M200/Mstar for red galaxies over 2.5 decades in stellar mass. We find a minimum for this ratio at Mstar ∼ 3-4 × 1010 h− 2 M⊙ with a strong increase for lower stellar masses.

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