Probing the azimuthal environment of galaxies around clusters. From cluster core to cosmic filaments

TL;DR

This study statistically analyzes the azimuthal distribution of galaxies around clusters, revealing filamentary structures and galaxy activity gradients, using harmonic decomposition on observational and simulated data across various cluster environments.

Contribution

It introduces a harmonic decomposition method to quantify galaxy distribution asymmetries around clusters and compares observational data with hydrodynamical simulations to understand filamentary structures.

Findings

Ellipsoidal galaxy distribution in inner cluster regions, more pronounced in richer clusters.

Detection of filamentary patterns in outskirts with a mean angular scale of 4.2.

Passive galaxies better trace filamentary structures, with increased star-forming activity farther from cluster centers.

Abstract

Galaxy clusters are connected at their peripheries to the large scale structures by cosmic filaments that funnel accreting material. These filamentary structures are studied to investigate both environment-driven galaxy evolution and structure formation and evolution. In the present work, we probe in a statistical manner the azimuthal distribution of galaxies around clusters as a function of the cluster-centric distance, the cluster richness, and the galaxy activity (star-forming or passive).We perform a harmonic decomposition in large photometric galaxy catalogue around 6400 SDSS clusters with masses M >1e14 solar masses, in the redshift range of 0.1< z <0.3. The same analysis is performed on the mock galaxy catalogue from the light-cone of Magneticum hydrodynamical simulation. We use the multipole analysis to quantify asymmetries in the 2-D galaxy distribution. In the inner cluster regions at R <2 R500, we confirm that the galaxy distribution traces an ellipsoidal shape, which is more pronounced for richest clusters. In the clusters' outskirts (R= [2-8]R500), filamentary patterns are detected in harmonic space with a mean angular scale m_mean= 4.2+/-0.1. Massive clusters seem to have a larger number of connected filaments than low massive ones. We also find that passive galaxies appear to better trace the filamentary structures around clusters, even if the contribution of SF ones tend to increase with the cluster-centric distance, suggesting a gradient of galaxy activity in filaments around clusters.