The Horologium Supercluster

The Horologium Supercluster is a gigantic supercluster with a length of about 550 million light years. This map shows every galaxy brighter than magnitude 17 (from the HyperLeda database) in this area of the sky. All of the major clusters of galaxies in the Horologium supercluster are marked. The nearest part of this supercluster (mainly the clusters near the bottom of the picture) is 700 million light years away but the far end (mainly the clusters at the top) is 1.2 billion light years from us. There are no other superclusters within a billion light years which are as big as this.

The Horologium Supercluster

Below is a list of the major clusters of galaxies in and near the Horologium Supercluster. There are about forty clusters in this list, which is a much greater quantity than most other superclusters. This list is probably not complete. There are a lot of other clusters in the Abell catalogue in this region of the sky which do not have a published redshift and hence have an unknown distance - a few of these clusters are probably also in the Horologium Supercluster.

   1           2       3        4         5       6      7               
 Abell         Equatorial    Redshift  Distance  Rich  Notes             
 Number       Coordinates       z        Mly                             
              RA       Dec                                               
 A3004      02 18.9  -48 00   .0619      840      0                      
 A3009      02 22.1  -48 34   .0641      865      1                      
 A3040      02 40.1  -55 25   .0920     1225      1    background cluster
 A3047      02 45.2  -46 27   .0938     1250      0    background cluster
 A3074      02 57.9  -52 43   .0718      965      0                      
 A3078      03 00.5  -51 50   .0636      860      0                      
 A3089      03 08.2  -36 43   .0655      885      0                      
 A3093      03 10.9  -47 24   .0818     1095      2                      
 A3098      03 13.7  -38 19   .0821     1100      0                      
 A3100      03 13.8  -47 48   .0617      835      0                      
 A3104      03 14.3  -45 25   .0718      965      0                      
 A3106      03 14.5  -58 06   .0627      850      0                      
 A3107      03 15.4  -42 46   .0863     1155      1                      
 A3108      03 15.2  -47 38   .0613      830      1                      
 A3109      03 16.7  -43 51   .0908     1210      0                      
 A3110      03 16.5  -50 54   .0737      990      0                      
 A3111      03 17.8  -45 44   .0763     1025      1                      
 A3112      03 17.9  -44 14   .0738      995      2                      
 A3116      03 19.0  -42 56   .0818     1095      0                      
 A3120      03 21.9  -51 19   .0678      915      0                      
 A3122      03 22.3  -41 20   .0631      855      2                      
 A3123      03 23.0  -52 01   .0632      855      0                      
 A3125      03 27.4  -53 31   .0577      785      0                      
 A3126      03 28.7  -55 43   .0844     1130      1                      
 A3128      03 30.2  -52 34   .0587      795      3    'Shapley 20'      
 A3133      03 32.7  -45 57   .0522      710      0                      
 A3135      03 34.0  -39 00   .0630      850      2                      
 A3140      03 36.3  -40 38   .0608      825      0                      
 A3144      03 37.1  -55 01   .0431      590      1    foreground cluster
 A3145      03 37.9  -38 01   .0592      805      0                      
 A3158      03 43.0  -53 39   .0585      795      2    'Shapley 17'      
 A3164      03 45.8  -57 03   .0558      760      0                      
 A3193      03 58.2  -52 20   .0345      475      0    foreground cluster
 A3195      03 59.2  -35 11   .0738      995      0                      
 A3202      04 00.2  -53 40   .0681      920      1                      
 A3223      04 08.6  -30 49   .0589      800      2                      
 A3225      04 09.3  -59 36   .0537      730      0                      
 A3266      04 31.2  -61 29   .0577      785      2                      
 A3301      05 00.8  -38 41   .0524      715      3                      
 A3312      05 03.9  -56 56   .0526      715      2                      

Below is a list of other major groups of galaxies in the vicinity of the Horologium supercluster. These are all groups which contain many tens of galaxies but which were not significant enough to be included in the Abell catalogue. This is a fairly random selection, there are a lot of groups in this area which do not have a published redshift. The foreground groups in this list are interesting because together with the A3144 and A3193 clusters they form part of a smaller supercluster in front of the Horologium supercluster at a distance of 550 million light years (redshift 0.040).

   1           2       3        4         5       6      7               
 Group         Equatorial    Redshift  Distance  Rich  Notes             
 Name         Coordinates       z        Mly                             
              RA       Dec                                               
 S239       02 16.8  -47 49   .0635      860                             
 S250       02 22.3  -51 06   .0484      660           foreground group  
 S261       02 25.2  -63 14   .0574      780                             
 S274       02 31.2  -57 56   .0309      425           foreground group  
 S315       02 59.2  -51 01   .0618      835                             
 S324       03 10.0  -47 20   .0585      795                             
 S329       03 12.6  -49 38   .0531      720                             
 S336       03 17.5  -44 42   .0744     1000                             
 S338       03 18.2  -52 15   .0384      525           foreground group  
 S339       03 19.3  -53 52   .0546      740                             
 S346       03 22.4  -49 19   .0670      905                             
 S353       03 26.4  -51 25   .0410      560           foreground group  
 S366       03 34.9  -53 35   .0598      810                             
 S367       03 35.5  -45 10   .0666      900                             
 S372       03 37.2  -55 25   .0758     1020                             
 S377       03 40.7  -55 12   .0425      580           foreground group  
 S390       03 47.0  -54 02   .0605      820                             
 S393       03 48.3  -45 33   .0454      620           foreground group  
 S399       03 54.5  -53 48   .0394      540           foreground group  
 S404       03 56.4  -53 52   .0365      500           foreground group  
 S412       04 01.7  -56 54   .0467      635           foreground group  
 S413       04 02.7  -63 48   .0370      505           foreground group  
 S416       04 04.8  -43 51   .0648      875                             
 S424       04 07.6  -43 25   .0589      800                             
 S433       04 14.5  -50 48   .0668      909                             
 S461       04 28.2  -50 32   .0539      735                             
 S463       04 29.2  -53 50   .0394      540           foreground group  
 S468       04 31.7  -46 07   .0675      910                             
 S479       04 37.8  -51 26   .0363      500           foreground group  
 S487       04 40.4  -44 38   .0372      510           foreground group  
 S497       04 46.1  -44 44   .0329      450           foreground group  
 S501       04 50.1  -51 08   .0768     1030                             
Column 1: The name/number of the cluster or group.
Column 2: The Right Ascension for epoch 2000.
Column 3: The Declination for epoch 2000.
Column 4: The redshift of the cluster.
Column 5: The distance in millions of light years assuming H=70km/s/Mpc.
Column 6: The 'richness' class of the cluster (for Abell clusters only).
Column 7: Additional names and notes.

References:
Abell G, Corwin H, Olowin R, (1989), A catalogue of Rich Clusters of Galaxies, 
          Astrophys J Supp, 70, 1.
Struble M, Rood H, (1999), A compilation of redshifts and velocity dispersions for 
          ACO clusters, Astrophys J, 125, 35.

Below is a map of the Horologium Supercluster. This map shows a side-view of the supercluster. All of the Abell clusters in and near the supercluster are labelled. The nearest part of the supercluster to us is at the top-right where the A3133 cluster is. This supercluster is much, much larger than most other superclusters. Compare this supercluster with the Perseus-Pisces supercluster which is fairly long but it only contains 3 rich clusters of galaxies. The Shapley supercluster contains a lot of rich clusters but it is also much smaller than the Horologium supercluster.

A map of the Horologium Supercluster
An animation of the Horologium Supercluster

This is an animation of the Horologium Supercluster. This animation shows all the major clusters of galaxies listed above which are in this supercluster. The Horologium supercluster is very long, but it is also very thin. The supercluster is a very long wall of galaxies which is filled with a lot of very rich clusters of galaxies.


Properties of the Horologium Supercluster (estimates)
Length of the supercluster 550 million light years
Mass of the supercluster 1017 solar masses
Number of galaxy groups in the supercluster 5 000
Number of large galaxies in the supercluster 30 000
Number of dwarf galaxies in the supercluster 300 000
Number of stars in the supercluster 1 million billion

A3128 - The Shapley 20 Cluster

Below is a picture of the centre of the A3128 cluster. This cluster was number twenty in a list of twenty-five rich clusters which Harlow Shapley published in 1933. This cluster does not contain any of the gigantic elliptical galaxies sometimes found at the centre of rich clusters although there are certainly a lot of large galaxies here. This is the richest cluster of galaxies in the Horologium supercluster and one of the richest clusters within a billion light years from us.

A3128 - from the Digitized Sky Survey
A map of the A3128 cluster

This is a map of the A3128 cluster. This map shows 128 of the brightest galaxies in this cluster. A few of these galaxies (including IC1946, IC1957 and PGC 12997) are foreground galaxies 250 million light years in front of the cluster. But most of the galaxies here (including IC1945) are in the cluster.



The Scientific Study of the Horologium Supercluster

In 1899, Edward Pickering reported that one of his astronomers (De Lisle Stewart) at the Harvard Observatory had noticed a very faint "group of nebulae" in the constellation of Horologium. Although they would never know it, this was the first observation of the Horologium supercluster.

The next person to notice the Horologium supercluster was Harlow Shapley. In 1935, he published A Catalogue of 7889 External Galaxies in Horologium and Surrounding Regions. He noticed some rich clusters of galaxies and he wrote that the "groups of galaxies in this region are only concentrations in an extensive cloud of galaxies". He published some maps of the region including this map. The three main clusters on the map correspond to the clusters A3128, A3158 and A3164.

The first attempt to study this supercluster after Harlow Shapley was made by J Lucey, R Dickens, R Mitchell and J Dawe in 1983. They published a paper called The Horologium-Reticulum supercluster of galaxies. They surveyed a small part of the supercluster and published a simple map showing that there are two superclusters here - a small supercluster at 550 million light years and a larger supercluster at 800 million light years. In 1984, G Chincarini, M Tarenghi, H Sol, P Crane, I Manousoyannaki and J Materne also studied this supercluster. Their survey was not very sensitive, and it only revealed the smaller, nearer supercluster.

The Horologium supercluster is a remarkable supercluster. It is one of the largest and richest superclusters known. However, since 1984 it has been completely ignored. Not many astronomers have heard of the Horologium supercluster and many of those who have heard of it seem to be unaware of how large it is. A few astronomers are aware of its size, but noone has studied it in detail. This web page seems to be the first serious (although brief) attempt to describe the entire supercluster.


Below - a picture of the centre of the A3158 cluster of galaxies. This is another of the very rich clusters of galaxies in the Horologium supercluster and it lies at exactly the same distance as the A3128 cluster. The three largest elliptical galaxies in this picture are (from right to left) PGC 13641, ESO 156-8, and PGC 13679.

A3158 - from the Digitized Sky Survey
The nearest superclusters Back to the Neighbouring Superclusters page