The SKA as a Doorway to Angular Momentum
  Angular momentum is one of the most fundamental physical quantities governing
galactic evolution. Differences in the colours, morphologies, star formation
rates and gas fractions amongst galaxies of equal stellar/baryon mass M are
potentially widely explained by variations in their specific stellar/baryon
angular momentum j. The enormous potential of angular momentum science is only
just being realised, thanks to the emergence of the first simulations of
galaxies with converged spins, paralleled by a dramatic increase in kinematic
observations. Such observations are still challenged by the fact that most of
the stellar/baryon angular momentum resides at large radii. In fact, the radius
that maximally contributes to the angular momentum of an exponential disk
(3Re-4Re) is twice as large as the radius that maximally contributes to the
disk mass; thus converged measurements of angular momentum require either
extremely deep IFS data or, alternatively, kinematic measurements of neutral
atomic hydrogen (HI), which naturally resides at the large disk radii that
dominate the angular momentum. The SKA has a unique opportunity to become the
world-leading facility for angular momentum studies due to its ability to
measure the resolved and/or global HI kinematics in very large and
well-characterised galaxy samples. These measurements will allow, for example,
(1) a very robust determination of the two-dimensional distribution of galaxies
in the (M,j)-plane, (2) the largest, systematic measurement of the relationship
between M, j, and tertiary galaxy properties, and (3) the most accurate
measurement of the large-scale distribution and environmental dependence of
angular momentum vectors, both in terms of norm and orientation. All these
measurements will represent exquisite tools to build a next generation of
galaxy evolution models.
