A halo mass—concentration relation from weak lensing

Abstract

We perform a statistical weak lensing analysis of dark matter profiles around tracers of halomass from galaxy-size to cluster-size halos. In this analysis we use 170 640 isolated∼L* galaxies split into ellipticals and spirals, 38 236 groups traced via isolated spectroscopicluminous red galaxies and 13 823 maxBCG clusters from the Sloan Digital Sky Surveycovering a wide range of richness. Together these three samples allow a determination ofthe density profiles of dark matter halos over three orders of magnitude in mass, from to . The resulting lensing signal is consistent with a Navarro–Frenk–White (NFW) or Einastoprofile on scales outside the central region. In the inner regions, uncertainty in modeling of theproper identification of the halo center and inclusion of baryonic effects from the centralgalaxy make the comparison less reliable. We find that the NFW concentration parameterc200b decreases with halo mass, from around 10 for galactic halos to 4 for cluster halos. Assuming itsdependence on halo mass in the form of we find c0 = 4.6 ± 0.7 (at z = 0.22)and β = 0.13 ± 0.07, with very similar results for the Einasto profile. The slope(β) is in agreement with theoretical predictions, while the amplitude is about two standarddeviations below the predictions for this mass and redshift, but we note thatthe published values in the literature differ at a level of 10–20% and that for aproper comparison our analysis should be repeated in simulations. We compare ourresults to other recent determinations, some of which find significantly higherconcentrations. We discuss the implications of our results for the baryonic effectson the shear power spectrum: since these are expected to increase the haloconcentration, the fact that we see no evidence of high concentrations on scales above20% of the virial radius suggests that baryonic effects are limited to small scales, and are not asignificant source of uncertainty for the current weak lensing measurements of the darkmatter power spectrum.