The Splashback Feature around DES Galaxy Clusters: Galaxy Density and Weak Lensing Profiles

TL;DR

This study detects the splashback feature in galaxy density and weak lensing profiles around DES galaxy clusters, providing new observational evidence for the boundary of dark matter halos and confirming predictions of the LCDM model.

Contribution

First measurement of the splashback feature in both galaxy density and matter profiles using DES data, confirming theoretical predictions and previous SDSS results.

Findings

Splashback radius measured at ~1.13 Mpc/h from galaxy density profiles.

Weak lensing data also shows a splashback-like steepening at ~1.34 Mpc/h.

Splashback radius scales with R_200m and is consistent across redshifts 0.3 to 0.6.

Abstract

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.