Gravitational lensing detection of an extremely dense environment around a galaxy cluster

Abstract

Galaxy clusters form at the highest density nodes of the cosmic web 1,2 . The clustering of massive halos is enhanced relative to the general mass distribution and matter beyond the virial region is strongly correlated to the halo mass (halo bias) 3 . Clustering can be further enhanced depending on halo properties other than mass (secondary bias) 4-7 . The questions of how much and why the regions surrounding rich clusters are over-dense are still unanswered [8][9][10][11][12][13] . Here, we report the analysis of the environment bias in a sample of very massive clusters, selected through the Sunyaev-Zel'dovich effect by the Planck mission 14,15 . We present the first detection of the correlated dark matter associated to a single cluster, PSZ2 G099.86+58.45. The system is extremely rare in the current paradigm of structure formation. The gravitational lensing signal was traced up to 30 megaparsecs with high signalto-noise ratio (∼ 3.4). The measured shear is very large and points at environment matter density in notable excess of the cosmological mean. The boosting of the correlated dark matter density around high mass halos can be very effective. Together with ensemble studies of the large scale structure, lensing surveys can picture the surroundings of single haloes.The environment bias be expresses the matter overdensity in the surroundings of massive halos. Observational campaigns have ascertained the halo bias and its mass dependence 8,9,13 but efforts to detect enhancing mechanisms or secondary biases for massive halos have been inconclusive. Contamination by foreground or background groups hampers the analysis in stacked cluster subsamples 11,12 . Here, we measure for the first time the environment bias of a single massive cluster by detection of the weak lensing (WL) signal. WL distorts the shape of the background galaxies. The correlated matter around the halo imprints a peculiar feature in the shear profile 16 . No proxy is needed. Mass and concentration of the halo and environment bias can be determined by fitting the shear profile up to very large distances. Even though the measurement of the shear around a single cluster is very challenging due to high noise, the interpretation is much more direct than for stacked samples, where the noise is reduced at the price of averaging over heterogeneous or contaminated samples.Sunyaev-Zel'dovich (SZ) selected galaxy clusters appear to be trustful tracers of the massive end of the cosmological halo mass function 17 . We studied the environment bias in the PSZ2LenS sample 15 , which consists of the 35 galaxy clusters detected by the Planck mission 14 in the sky portion covered by the lensing surveys CFHTLenS (Canada France Hawaii Telescope Lensing Survey) 18 and RCSLenS (Red Cluster Sequence Lensing Survey) 19 . PSZ2LenS is a statistically complete and homogeneous subsample of the PSZ2 14 catalogue. It is approximately mass limited and the main halo properties are in excellent agreement with the ΛCDM (Cold Dark Matter with a cosmological constant Λ) scenario of ...

LOFAR Discovery of a Radio Halo in the High-redshift Galaxy Cluster PSZ2 G099.86+58.45

“…At the same time it should be stressed that PSZ2G099 is sitting in a special region of the Universe, which was found to be about six times denser than the average density of the Universe at that redshift (Sereno et al 2018); its RH could therefore be unique. The effect of the large-scale environment (environment-bias; see Mao et al 2018, and ref.…”

“…PSZ2G099 is a massive, M 500 = (6.84±0.48)×10 14 M (Planck Collaboration et al 2016) and hot, kT = 8.9 +2.8 −1.1 keV (Sereno et al 2018) cluster discovered through its Sunyaev-Zel'dovich (SZ) signal by the Planck satellite. Recently, the gravitational lensing signal of this cluster has been traced up to 30 Mpc from its centre implying that it sits in a very high-density environment, about six times denser than the average ΛCDM prediction at this redshift (Sereno et al 2018). The expected complex dynamics around this cluster make the discovery of a RH in this cluster particularly interesting.…”

AMICO galaxy clusters in KiDS-DR3: weak lensing mass calibration

“…This cut was originally proposed by Oguri et al (2012) based on the properties of the galaxies in the COSMOS catalogue (Ilbert et al 2009) to select galaxies at z 0.7, and has been subsequently tested and used by Covone et al (2014), Sereno et al (2017Sereno et al ( , 2018a. In particular, Sereno et al (2017) showed that the 97% of the galaxies with high quality spectroscopic redshifts selected by this cut in the CFHTLS-W1 and W4 fields have z spec > 0.63.…”

Einstein, Planck and Vera Rubin: Relevant Encounters Between the Cosmological and the Quantum Worlds

“…However, the work in ref. 273 recently reported the first detection of an extremely dense environment around a massive galaxy cluster, PSZ2 G099.86 + 58.45, located at redshift z 0.616, from the PSZ2LenS [274] cluster sample. PSZ2LenS is a small but homogeneous and complete sample of 35 galaxy clusters, detected by the Planck mission in the sky regions observed by the CFHTLenS (Canada-France-Hawaii Telescope Lensing Survey) [275] and RCSLenS (Red Cluster Sequence Lensing Survey) [276].…”