2018MNRAS.474..866V

Galaxy systems with large magnitude gaps - defined as the difference in magnitude between the central galaxy and the brightest satellite in the central region, such as fossil groups - are claimed to have earlier formation times. In this study, we measure the mass concentration, as an indicator of the formation epoch, of ensembles of galaxy systems divided by redshift and magnitude gaps in the r band. We use cross-correlation weak-lensing measurements with NFW parametric mass profiles to measure masses and concentrations of these ensembles from a catalogue of systems built from the SDSS Coadd by the redMaPPer algorithm. The lensing shear data come from the CFHT Stripe 82 (CS82) survey, and consists of i-band images of the SDSS Stripe 82 region. We find that the stack made up of systems with larger magnitude gaps has a high probability of being more concentrated, in the lowest redshift slice (0.2 < z < 0.4), both when dividing in quartiles (P = 0.98) and tertiles (P = 0.85). These results lend credibility to the claim that systems with large magnitude gaps tend to have been formed early.