Splashback refers to the process of matter that is accreting onto a dark matter halo reaching its first orbital apocenter and turning around in its orbit .
The cluster-centric radius at which this process occurs , r _ { sp } , defines a halo boundary that is connected to the dynamics of the cluster .
A rapid decline in the halo profile is expected near r _ { sp } .
We measure the galaxy number density and weak lensing mass profiles around redMaPPer galaxy clusters in the first year Dark Energy Survey ( DES ) data .
For a cluster sample with mean M _ { 200 m } mass \approx 2.5 \times 10 ^ { 14 } M _ { \odot } , we find strong evidence of a splashback-like steepening of the galaxy density profile and measure r _ { sp } = 1.13 \pm 0.07 h ^ { -1 } Mpc , consistent with earlier SDSS measurements of \citet More2016 and \citet Baxter2017 .
Moreover , our weak lensing measurement demonstrates for the first time the existence of a splashback-like steepening of the matter profile of galaxy clusters .
We measure r _ { sp } = 1.34 \pm 0.21 h ^ { -1 } Mpc from the weak lensing data , in good agreement with our galaxy density measurements .
For different cluster and galaxy samples , we find that consistent with \Lambda CDM simulations , r _ { sp } scales with R _ { 200 m } and does not evolve with redshift over the redshift range of 0.3–0.6 .
We also find that potential systematic effects associated with the redMaPPer algorithm may impact the location of r _ { sp } .
We discuss progress needed to understand the systematic uncertainties and fully exploit forthcoming data from DES and future surveys , emphasizing the importance of more realistic mock catalogs and independent cluster samples .