Midlife crises in dwarf galaxies in the NGC5353/4 group

This third paper in a series about the dwarf galaxy populations in groups within the Local Supercluster concerns the intermediate mass (2.1 x 10(13) M circle dot) NGC5353/4 Group with a core dominated by S0 systems and a periphery of mostly spiral systems. Dwarf galaxies are strongly concentrated toward the core. The mass-to-light ratio M/LR = 105M circle dot/L circle dot is a factor of 3 lower than for the two groups studied earlier in the series. The properties of the group suggest it is much less dynamically evolved than those two groups of early-type galaxies. By comparison, the NGC5353/4 Group lacks superluminous systems but has a large fraction of intermediate-luminosity galaxies; or equivalently, a luminosity function with a flatter faint-end slope. The luminosity function for the NGC5353/4 Group should steepen as the intermediate-luminosity galaxies merge. Evidence for the ongoing collapse of the group is provided by the unusually large incidence of star-formation activity in small galaxies with early morphological types. The pattern in the distribution of galaxies with activity suggests a succession of infall events. Residual gas in dwarfs that enter the group is used up in sputtering events. The resolution of midlife crises is exhaustion.