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 \times 10 ^ { ~ { } 11 } M _ { \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 _ { * } = 3.4 M _ { * } ^ { 1.26 \pm 0.06 } , 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 _ { c } = 6.4 v _ { max } ^ { 0.64 \pm 0.04 } .
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 } \sim 0.70 ) than thick ones ( f _ { j } \sim 0.40 ) .
Stellar haloes have their progenitor baryons assembled the latest ( z _ { ~ { } 1 / 2 } \sim 1.1 ) and over the longest timescales ( \tau \sim 6.2 Gyr ) , and have the smallest fraction of stars born in-situ ( f _ { in - situ } = 0.35 \pm 0.14 ) .
All other structures have 1.5 \lesssim z _ { 1 / 2 } \lesssim 3 , \tau = 4 \pm 2 Gyr and f _ { in - situ } \gtrsim 0.9 .