Substructure and dynamics of the Fornax Cluster

We present the first dynamical analysis of a galaxy cluster to include a la rge fraction of dwarf galaxies. Our sample of 108 Fornax Cluster members me asured with the UK Schmidt Telescope FLAIR-II spectrograph contains 55 dwar f galaxies (15.5 > b(j) > 18.0 or -16 > M-B > -13.5). H alpha emission show s that of the dwarfs are star forming, twice the fraction implied by morpho logical classifications. The total sample has a mean velocity of 1493 +/- 3 6 kms s(-1) and a velocity dispersion of 374 +/- 26 km s(-1). The dwarf gal axies form a distinct population: their velocity dispersion (429 +/- 41 km s(-1)) is larger than that of the giants () at the 98% confidence level. Th is suggests that the dwarf population is dominated by infalling objects whe reas the giants are virialized. The Fornax system has two components, the m ain Fornax Cluster centered on NGC 1399 with cz = 1478 km s(-1) and sigma ( cz) = 370 km s(-1) and a subcluster centered 3 degrees to the southwest inc luding NGC 1316 with cz = 1583 km s(-1) and sigma (cz) = 377 km s(-1). This partition is preferred over a single cluster at the 99% confidence level. The subcluster, a site of intense star formation, is bound to Fornax and pr obably infalling toward the cluster core for the first time. We discuss the implications of this substructure for distance estimates of the Fornax Clu ster. We determine the cluster mass profile using the method of Diaferio, w hich does not assume a virialized sample. The mass within a projected radiu s of 1.4 Mpc is (7 +/- 2) x 10(13) M-., and the mass-to-light ratio is 300 +/- 100 M-./L-.. The mass is consistent with values derived from the projec ted mass virial estimator and X-ray measurements at smaller radii.