The Splashback Feature around DES Galaxy Clusters: Galaxy Density and
  Weak Lensing Profiles
  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_200m mass
~2.5 x 10^14 M_sun, we find strong evidence of a splashback-like steepening of
the galaxy density profile and measure r_sp=1.13 +/- 0.07 Mpc/h, consistent
with earlier SDSS measurements of More et al. (2016) and Baxter et al. (2017).
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 +/- 0.21 Mpc/h from the weak lensing data, in
good agreement with our galaxy density measurements. For different cluster and
galaxy samples, we find that consistent with LCDM simulations, r_sp scales with
R_200m 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.
