Substructure and Dynamics of the Fornax Cluster

We present the first dynamical analysis of a galaxy cluster to include a large fraction of dwarf galaxies. Our sample of 108 Fornax Cluster members measured with the UK Schmidt Telescope FLAIR-II spectrograph contains 55 dwarf galaxies ( or ). Ha emission shows that of the dwarfs are 15.5 1 b 1 18.0 216 1 M 1 213.5 36% 5 8% J B star forming, twice the fraction implied by morphological classifications. The total sample has a mean velocity of and a velocity dispersion of . The dwarf galaxies form a distinct population: 21 21 1493 5 36 km s 374 5 26 km s their velocity dispersion ( ) is larger than that of the giants ( ) at the 98% con21 21 429 5 41 km s 308 5 30 km s fidence level. This suggests that the dwarf population is dominated by infalling objects whereas the giants are virialized. The Fornax system has two components, the main Fornax Cluster centered on NGC 1399 with cz p and and a subcluster centered 37 to the southwest including NGC 1316 with 21 21 1478 km s j p 370 km s cz and . This partition is preferred over a single cluster at the 99% confidence 21 21 cz p 1583 km s j p 377 km s cz level. The subcluster, a site of intense star formation, is bound to Fornax and probably infalling toward the cluster core for the first time. We discuss the implications of this substructure for distance estimates of the Fornax Cluster. We determine the cluster mass profile using the method of Diaferio, which does not assume a virialized sample. The mass within a projected radius of 1.4 Mpc is , and the mass-to-light ratio is 13 (7 5 2) # 10 M 300 5 , . The mass is consistent with values derived from the projected mass virial estimator and X-ray 100 M /L , , measurements at smaller radii. Subject headings: distance scale — galaxies: clusters: general — galaxies: clusters: individual (Fornax)