Fornax Cluster
The Fornax cluster of galaxies is a large collection of galaxies, the chemical in the constellation oven ( Fornax ) distributed over an area of about 5 ° angular diameter is. In the catalog of George Ogden Abell He may be found under the name Abell S0373.
This cluster is at a distance of about 60 million light- years ( 18.5 Mpc ) the second richest clusters within a distance of 100 million light- years in size surpassed only by about three times as large Virgo cluster of galaxies. It contains about 50-60 brighter galaxies, three of which are among the largest galaxies in this part of the universe. The elliptical galaxy NGC 1399 is a cD galaxy with extended diffuse halo, as they typically occur in rich clusters of galaxies (eg in the Coma cluster of galaxies ). The large barred spiral galaxy NGC 1365 can be seen as a prototype of this class of galaxies and as such is the most prominent member of the cluster. The largest member of the Fornax cluster is the giant lenticular galaxy NGC 1316, which may be an apparent magnitude of 8.4 and has an angular diameter of 12 arc minutes. This galaxy is at a frequency of 1400 MHz, the fourth strongest radio source in the sky and is therefore also known as Fornax A.
Distance determination
The Fornax cluster of galaxies is of great importance for the cosmological distance determination. Since he has a much smaller mass than the approximately equidistant Virgo cluster, its gravitational influence on our Local Group is far lower. During the Virgo cluster by its large mass attraction of the Local Group causes (English Virgo infall ), the the Fornax cluster moves largely with the large-scale Hubble flow. A direct distance determination of galaxies in the Fornax cluster can therefore be determined from its redshift, the Hubble constant. The relatively small distance of the cluster are now several direct methods of Entfernungsbstimmung available. The globular cluster luminosity function ( engl. globular cluster luminosity function, GCLF ) is the distance in 1996 to be about 16.5 Mpc. Succeeded in 1998 by the Hubble Space Telescope also judge the distance of the cluster by the single star resolution of variable stars of the Cepheid type. From these measurements, the results today adopted value of the distance of the Fornax cluster of 18.5 Mpc. The mean redshift of the cluster members is equivalent to a gravitational velocity of about 1300 km / s, so that the determined from these measurements Hubble constant gives (after some corrections) H0 = 73 km / ( s · Mpc ).