Measurement of the splashback feature around SZ-selected Galaxy clusters with DES, SPT, and ACT

Abstract

We present a detection of the splashback feature around galaxy clusters selected using the Sunyaev–Zel’dovich (SZ) signal. Recent measurements of the splashback feature around optically selected galaxy clusters have found that the splashback radius, rsp, is smaller than predicted by N-body simulations. A possible explanation for this discrepancy is that rsp inferred from the observed radial distribution of galaxies is affected by selection effects related to the optical cluster-finding algorithms. We test this possibility by measuring the splashback feature in clusters selected via the SZ effect in data from the South Pole Telescope SZ survey and the Atacama Cosmology Telescope Polarimeter survey. The measurement is accomplished by correlating these cluster samples with galaxies detected in the Dark Energy Survey Year 3 data. The SZ observable used to select clusters in this analysis is expected to have a tighter correlation with halo mass and to be more immune to projection effects and aperture-induced biases, potentially ameliorating causes of systematic error for optically selected clusters. We find that the measured rsp for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters makes a precise comparison difficult. In agreement with previous work, when using optically selected redMaPPer clusters with similar mass and redshift distributions, rsp is ∼2σ smaller than in the simulations. These results motivate detailed investigations of selection biases in optically selected cluster catalogues and exploration of the splashback feature around larger samples of SZ-selected clusters. Additionally, we investigate trends in the galaxy profile and splashback feature as a function of galaxy colour, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first infall into the cluster.

Cluster–galaxy weak lensing

“…Chang et al (2018) found that r sp measured from weak lensing is smaller than but consistent with the expectation from N-body simulations within the large errors. The r sp measured from the galaxy density profile with a higher precision is significantly smaller than that determined from the corresponding population of subhalos in N-body simulations (see also Shin et al 2019), which is in agreement with the previous results based on the SDSS redMaPPer samples (More et al 2016;Baxter et al 2017). Using N-body simulations, Chang et al (2018) found that the effect of dynamical friction is significant only for very massive subhalos and the fiducial galaxy sample used in their analysis is likely not significantly affected by dynamical friction.…”

“…Since the efficiency of dynamical friction increases with the ratio of subhalo to cluster halo mass, the impact of dynamical friction on the splashback feature is expected to depend on the luminosity of tracer galaxies (e.g., More et al 2016;Chang et al 2018). The splashback feature in stacked galaxy surface density profiles has been routinely detected using cluster-galaxy cross correlations, thanks to statistical samples of clusters defined from large optical or SZE surveys (More et al 2016;Baxter et al 2017;Chang et al 2018;Shin et al 2019;Zürcher and More 2019;Murata et al 2020).…”

The edge of the Galaxy

“…Interestingly, there is now considerable evidence that splashback radii have been measured observationally in the outskirts of galaxy clusters (e.g. More et al 2016;Baxter et al 2017;Chang et al 2018;Contigiani, Hoekstra & Bahé 2019;Shin et al 2019;Zürcher & More 2019;Murata et al 2020). While the measured splashback radii tend to be smaller than those predicted in CDM simulations, these results are still subject to systematic effects (Busch & White 2017;Xhakaj et al 2019;Murata et al 2020).…”

Splashback radius in symmetron gravity

“…Our results therefore imply that this feature can be used to constrain fifth forces with vacuum Compton wavelength λ 0 just below the Mpc scale. Because measurements of splashback in the galaxy distribution around clusters have already achieved a precision below the size of our predicted effect [16][17][18][19], we expect to soon be able to constrain not only the symmetron, but other fifth force models on similar scales.…”

“…This technique, known as lensing, has been used to measure the splashback feature around clusters [14,15]. It should be noted however that the most stringent constraints are obtained using the distribution of subhaloes traced by the cluster galaxy members [16][17][18][19]. In this case the interpretation is nevertheless not straightforward and an accurate comparison with Nbody ΛCDM simulations is required.…”