  Understanding how galaxies obtain baryons, their stars and gas, over cosmic
time is traditionally approached in two different ways - theoretically and
observationally. In general, observational approaches to galaxy formation
include measuring basic galaxy properties, such as luminosities, stellar
masses, rotation speeds, star formation rates and how these features evolve
through time. Theoretically, cosmologically based models collate the physical
effects driving galaxy assembly - mergers of galaxies, accretion of gas, star
formation, and feedback, amongst others, to form predictions which are matched
to galaxy observables. An alternative approach is to examine directly, in an
observational way, the processes driving galaxy assembly, including the effects
of feedback. This is a new `third way' towards understanding how galaxies are
forming from gas accretion and mergers, and directly probes these effects
instead of relying on simulations designed to reproduce observations. This
empirical approach towards understanding galaxy formation, including the
acquisition history of baryons, displays some significant differences with the
latest galaxy formation models, in addition to directly demonstrating the
mechanisms by which galaxies form most of their baryonic mass.

Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies