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Free keywords:
methods: numerical
galaxies: fundamental parameters
galaxies:
kinematics and dynamics
galaxies: stellar content
galaxies: structure
Astrophysics - Astrophysics of Galaxies
Abstract:
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× 10^ 11 M_{\odot }, all galaxies have a classical bulge and 70 per cent have a thin and thick disc. The kinematic (thin) discs follow a power-law relation between angular momentum and stellar mass J_*=3.4M_*^{1.26± 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=6.4v_max^{0.64± 0.04}. Tracing back in time these structures' progenitors, we find all of them to lose a fraction 1 - fj of their maximum angular momentum. Thin discs are significantly better at retaining their high- redshift spins (fj ̃ 0.70) than thick ones (fj ̃ 0.40). Stellar haloes have their progenitor baryons assembled the latest (z1/2 ̃ 1.1) and over the longest time-scales (τ ̃ 6.2 Gyr), and have the smallest fraction of stars born in situ (fin situ = 0.35 ± 0.14). All other structures have 1.5 ≲ z1/2 ≲ 3, τ = 4 ± 2 Gyr, and fin situ ≳ 0.9.
