The Evolution of Galaxy Structure over Cosmic Time
  I present a comprehensive review of the evolution of galaxy structure in the
universe from the first galaxies we can currently observe at z~6 down to
galaxies we see in the local universe. I further address how these changes
reveal galaxy formation processes that galaxy structural analyses can provide.
This review is pedagogical and begins with a detailed discussion of the major
methods in which galaxies are studied morphologically and structurally. This
includes the well-established visual method; Sersic fitting to measure galaxy
sizes and surface brightness profile shapes; non-parametric structural methods
including the concentration (C), asymmetry (A), clumpiness (S) (CAS) method, as
well as newer structural indices. Included is a discussion of how these
structural indices measure fundamental properties of galaxies such as their
scale, star formation rate, and ongoing merger activity. Extensive
observational results are shown demonstrating how broad galaxy morphologies and
structures change with time up to z~3, from small, compact and peculiar systems
in the distant universe to the formation of the Hubble sequence we find today.
This review further addresses how structural methods measure accurately the
merger history out to z~3. The properties and evolution of bulges, disks, bars,
and at z>1 large star forming clumps are also described, along with how
morphological galaxy quenching occurs. Furthermore, the role of environment in
producing structure in galaxies over cosmic time is treated. Alongside the
evolution of general structure, I also delineate how galaxy sizes change with
time, with measured sizes up to a factor of 2-5 smaller at high redshift at a
given stellar mass. This review concludes with a discussion of how galaxy
structure reveals the formation mechanisms behind galaxies, providing a new and
unique way to test theories of galaxy formation.
