Low Density Structures in the Local Universe. I. Diffuse Agglomerates of Galaxies

TL;DR

This study identifies and characterizes diffuse, low-density galaxy agglomerates in the local universe, revealing their properties and distribution using a percolation method on a large galaxy sample.

Contribution

First comprehensive analysis of diffuse galaxy agglomerates in low density regions using percolation, highlighting their properties and spatial distribution.

Findings

226 diffuse agglomerates identified with n>=4 members

Most agglomerates have median velocity dispersion of 170 km/s

Agglomerates have a median size of about 6 Mpc

Abstract

This paper is the first of a series considering the properties of distribution of nearby galaxies in the low density regions. Among 7596 galaxies with radial velocities V_{LG}<3500 km/s, absolute magnitudes M_K<-18.4^m$, and Galactic latitudes |b| >15 degr there are 3168 field galaxies (i.e. 42%) that do not belong to pairs, groups or clusters in the Local universe. Applying to this sample the percolation method with a radius of r_0=2.8 Mpc, we found 226 diffuse agglomerates with n>=4 number of members. The structures of eight most populated objects among them (n>=25) are discussed. These non-virialized agglomerates are characterized by a median dispersion of radial velocities of about 170 km/s, the linear size of around 6 Mpc, integral K-band luminosity of 3*10^{11} L_sun, and a formal virial-mass-to-luminosity ratio of about 700 M_sun/L_sun. The mean density contrast for the considered agglomerates is only <Delta n/\bar{n}\gtrsim 5, and their crossing time is about 30-40 Gyr.