NIHAO XVI: The properties and evolution of kinematically selected discs,
  bulges and stellar haloes
  We use 25 simulated galaxies from the NIHAO project to define and
characterize a variety of kinematic stellar structures: thin and thick discs,
large scale single discs, classical and pseudo bulges, spheroids, inner discs,
and stellar haloes. These structures have masses, spins, shapes and rotational
support in good agreement with theoretical expectations and observational data.
Above a dark matter halo mass of $2.5\times10^{\rm~11}M_{\rm\odot}$, all
galaxies have a classical bulge and 70\% have a thin and thick disc. The
kinematic (thin) discs follow a power-law relation between angular momentum and
stellar mass $J_{\rm *}=3.4M_{\rm *}^{\rm1.26\pm0.06}$, in very good agreement
with the prediction based on the empirical stellar-to-halo mass relation in the
same mass range, and show a strong correlation between maximum `observed'
rotation velocity and dark matter halo circular velocity $v_{\rm c}=6.4v_{\rm
max}^{0.64\pm0.04}$. Tracing back in time these structures' progenitors, we
find all to lose a fraction $1-f_j$ of their maximum angular momentum. Thin
discs are significantly better at retaining their high-redshift spins
($f_j\sim0.70$) than thick ones ($f_j\sim0.40$). Stellar haloes have their
progenitor baryons assembled the latest ($z_{\rm~1/2}\sim1.1$) and over the
longest timescales ($\tau\sim6.2$~Gyr), and have the smallest fraction of stars
born in-situ ($f_{\rm in-situ}=0.35\pm0.14$). All other structures have
$1.5\lesssim z_{\rm1/2}\lesssim3$, $\tau=4\pm2$~Gyr and $f_{\rm
in-situ}\gtrsim0.9$.
