Galaxy Groups within 3500 km s$^{-1}$

Understand

A study of the group properties of galaxies in our immediate neighborhood provides a singular opportunity to observationally constrain the halo mass function, a fundamental characterization of galaxy formation.

• Detailed studies of individual groups have provided the coefficients of scaling relations between a proxy for the virial radius, velocity dispersion, and mass that usefully allows groups to be defined over the range $10^{10} - 10^{15}$ $M_\odot$.
• At a second hierarchical level, associations are defined as regions around collapsed halos extending to the zero velocity surface at the decoupling from cosmic expansion.
• The most remarkable result of the study emerges from the construction of the halo mass function from the sample.