Density profiles of galaxy groups and clusters from SDSS galaxy-galaxy   weak lensing
  We present results of a measurement of the shape of the density profile of galaxy groups and clusters traced by 43 335 Luminous Red Galaxies (LRGs) with spectroscopic redshifts from the Sloan Digital Sky Survey (SDSS). The galaxies are selected such that they are the brightest within a cylindrical aperture, split into two luminosity samples, and modeled as the sum of stellar and dark matter components. We present a detailed investigation of many possible systematic effects that could contaminate our signal and develop methods to remove them, including a detected intrinsic alignment for galaxies within 100 kpc/h of LRGs which we remove using photometric redshift information. The resulting lensing signal is consistent with NFW profile dark matter halos; the SIS profile is ruled out at the 96 (conservatively) and 99.96 per cent confidence level (CL) for the fainter and brighter lens samples (respectively) when we fit using lensing data between 40 kpc/h and 2 Mpc/h with total signal-to-noise of 19 and 25 for the two lens samples. The lensing signal amplitude suggests that the faint and bright sample galaxies typically reside in haloes of mass (2.9+/-0.4)x10^{13} M_{sun}/h and (6.7+/-0.8)x10^{13} M_{sun}/h respectively, in good agreement with predictions based on halo spatial density with normalization lower than the 'concordance' sigma_8=0.9. When fitting for the concentration parameter in the NFW profile, we find c = 5.0+/-0.6 (stat) +/-1 (sys), and c = 5.6+/-0.6 (stat) +/-1 (sys) for the faint and bright samples, consistent with Lambda-CDM simulations. We also split the bright sample further to determine masses and concentrations for cluster-mass halos, finding mass (1.3+/-0.2)x10^{14} M_{sun}/h for the sample of LRGs brighter than -22.6 in r. (Abridged) 
Rachel Mandelbaum, Uros Seljak, Richard J. Cool, Michael Blanton,   Christopher M. Hirata, Jonathan Brinkmann