Beyond the Galaxy: Overview

Introduction

In exploring the realm beyond our Milky Way galaxy, Galaxies3D explores:

 

Galaxy Subgroups, Groups and Clusters

The Local Group of galaxies includes over 50 galaxies, dominated by two large spiral galaxies, the Andromeda galaxy (Messier 31, the largest galaxy of the Local Group), and the Milky Way. Numerous satellite galaxies orbit the Milky Way, forming the Milky Way subgroup of galaxies. The Andromeda galaxy also commands numerous satellites, forming an Andromeda subgroup of galaxies. NGC 3109, a Magellanic spiral (type SBm) on the Virgo Cluster side of the Local Group commands a small third subgroup:

Here is a view of the Milky Way subgroup of galaxies:

Milky Way Subgroup of Galaxies

Here is a view of the entire Local Group of Galaxies:

Local Group of Galaxies

In deplicting our neighboring galaxy groups and clusters, Galaxies3D uses the dominant galaxies in a group as surrogates to mark the location of the galaxy group:

Galaxy Groups Closer Than the Virgo Cluster

 

Superclusters

Use of a sphere to mark the position of a star is quite clear, and its use to show the position of a galaxy, or even a galaxy group, straightforward. However it becomes problematic when we use a sphere to mark a supercluster — a cluster of galaxy groups and galaxy clusters.

Galaxies and groups and clusters of galaxies are arranged in great intersecting filaments or sheets, forming a web or lattice-like structure throughout the universe. Superclusters are the intersections of these great filaments or sheets of galaxies. Between the great sheets and filaments of galaxies lie great voids containing just a few isolated galaxies. This web or lattice-like structure can be seen in this plot of galaxies from the Sloan Digital Sky Survey:

Sloan Digital Sky Survey Slice of the Universe

A slice through the Sloan Digital Sky Survey map of the distribution of galaxies (mapped in equatorial coordinates), showing all galaxies within -1.25 and 1.25 degrees declination.
Galaxies are colored according to the ages of their stars, with the redder, more strongly clustered points showing galaxies that are made of older stars.
The redshifts in the original Sloan diagram have been replaced with distances in Gly, using Ned Wright's Javascript Cosmology calculator.

Superclusters might be thought of as great metropolitan centers, connected by lines of many small towns and small cities along roads and highways. Between the network of highways and roads lie great rural voids containing just a rare, isolated farmhouse or shack. The sphere used by Galaxies3D to mark a supercluster might be thought of as like the dot marking a great metropolis on a map. The dot by no means delivers any sense of the sprawl and grandeur of the metropolis. Nonetheless, the dot does give us a sense of where that metropolis lies in relation to other metropolises.

With this in mind, compare this volume rendering of the density contours of galaxies forming several labeled superclusters from the paper by Brent Tully et al describing the Laniakea supercluster:

Region of Laniakea Supercluster

Fig ED 1 from Tully et al, Nature, vol 513, number 7516, p.71 (4 September 2014). Colors are inverted from original image. Norma is part of the Hydra-Centaurus Supercluster. Videos and 3D renderings from the Cosmic Flows group of the Laniakea supercluster and surrounding area can be found at the Cosmic Flows home page, on Vimeo (Cosmography of the Local Universe), and on Sketchfab (The Cosmic V-Web).

with a view of the same volume in Galaxies3D. Rather than using contour surfaces of galaxy density to deplict the superclusters, Galaxies3D uses the dominant rich galaxy clusters (the "A" prefix refers to a cluster's number in George Abell's catalog of rich galaxy clusters) in a supercluster as surrogates to mark the location of the supercluster:

The following image in the supergalactic plane (the SGX-SGY plane, SGZ = 0) adapted from the Cosmic Flows group paints the base grids of the Galaxies3D views of Nearby Superclusters and Rich Superclusters. The image color-codes the density of galaxies, red in the regions of highest density, blue in void regions. White lines identify streamlines of motion:

Cosmic Flows image of Galaxy Density and Flow Streamlines in the area of the Laniakea Supercluster and Surrounding Region

The Galaxies3D view of nearby Rich Superclusters within 1.5 Gly is based on the catalog of superclusters by Einasto et al (Astron. J. 122, 2222 (2001)). It includes:

  • all superclusters within 1.5 Gly with 7 or greater members
  • 5 additional named supraclusters with less than 7 members: Phoenix, Sextans (part of Sloan Great Wall), Hydra-Centaurus, Perseus-Pisces, and Coma (the latter 3 included to provide a reference for comparision with the Galaxies3D view of Nearby Superclusters)

The Galaxies3D view of Rich Superclusters within 1.5 Gly can be compared to the Galaxies3D view of Nearby Superclusters; both views show the Shapley, Hydra-Centaurus, Perseus-Pisces, Hercules, Coma, and Virgo (Local) superclusters. The Nearby Superclusters view (lower two images) expands the middle section of the Rich Supercluster view (upper image):

 

Beyond Our Galaxy