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 ( 15.5 > \hbox { $b _ { J } $ } > 18.0 or -16 > M _ { B } > -13.5 ) .
H \alpha emission shows that 36 \pm 8 \% of the dwarfs are star-forming , twice the fraction implied by morphological classifications .
The total sample has a mean velocity of 1493 \pm 36 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } and a velocity dispersion of 374 \pm 26 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } .
The dwarf galaxies form a distinct population : their velocity dispersion ( 429 \pm 41 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } ) is larger than that of the giants ( 308 \pm 30 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } ) at the 98 % confidence 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 \overline { cz } = 1478 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } and \sigma _ { cz } = 370 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } , and a subcluster centered 3 degrees to the south-west including NGC 1316 with \overline { cz } = 1583 \hbox { $ { \thinspace km } { \thinspace s } ^ { -1 } $ } and \sigma _ { cz } = 377 \hbox { $ { \thinspace km } { \thinspace 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 probably infalling towards 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 ( 6 ) , which does not assume a virialized sample .
The mass within a projected radius of 1.4 \thinspace Mpc is ( 7 \pm 2 ) \times 10 ^ { 13 } \hbox { $ { \thinspace M } _ { \sun } $ } , and the mass-to-light ratio is 300 \pm 100 \hbox { $ { \thinspace M } _ { \sun } $ } / \hbox { $ { \thinspace L } _ { \sun } $ } .
The mass is consistent with values derived from the projected mass virial estimator and X-ray measurements at smaller radii .