The Structure of Clusters with Bimodal Distributions of Galaxy Radial Velocities. II: A1775

TL;DR

This study investigates the bimodal velocity distribution of galaxies in Abell 1775, revealing it comprises two independent clusters with distinct distances, masses, and velocities, using photometric and spectroscopic data.

Contribution

The paper provides a detailed analysis of Abell 1775's bimodal structure, confirming it as two separate clusters with independent distances and properties, based on multiple observational methods.

Findings

A1775 consists of two independent clusters, A1775A and A1775B.

Each subcluster is at its own Hubble distance with small peculiar velocities.

Masses and luminosity-to-mass ratios are quantified for both subclusters.

Abstract

We analyze the structure of the cluster of galaxies Abell 1775 (13h42m, +26d22', cz ~ 21000 km/s), which exhibits a bimodal distribution of radial velocities of the containing galaxies. The difference of the subcluster radial velocities is \Delta V\approx 2900 km/s. We use the results of our photometric observations made with the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the spectroscopic and photometric data from the SDSS DR6 catalog to determine independent distances to the subclusters via three different methods: the Kormendy relation, photometric plane, and fundamental plane. We find that the A1775 cluster consists of two independent clusters, A1775A (cz=19664 km/s) and A1775B (cz=22576 km/s), each located at its own Hubble distance and having small peculiar velocities. Given the velocity dispersions of 324 km/s and 581 km/s and the dynamic masses within the R_200 radius equal to 0.6 10^14 and 3.3 10^14 M_sun, the A1775A and A1775B clusters have the K-band luminosity-to-mass ratios of 29 and 61, respectively. A radio galaxy with an extended tail belongs to the A1775B cluster.