Abstract
Detailed studies of galaxy formation require clear definitions of the structural components of galaxies. Precisely defined components also enable better comparisons between observations and simulations. We use a subsample of 18 cosmological zoom-in simulations from the Numerical Investigation of a Hundred Astrophysical Objects (NIHAO) project to derive a robust method for defining stellar kinematic discs in galaxies. Our method uses Gaussian Mixture Models in a 3D space of dynamical variables. The NIHAO galaxies have the right stellar mass for their halo mass, and their angular momenta and Sérsic indices match observations. While the photometric disc-to-total ratios are close to 1 for all the simulated galaxies, the kinematic ratios are around ~0.5. Thus, exponential structure does not imply a cold kinematic disc. Above M* ~ 109.5 M⊙, the decomposition leads to thin discs and spheroids that have clearly different properties, in terms of angular momentum, rotational support, ellipticity, [Fe/H] and [O/Fe]. At M* ≲ 109.5 M⊙, the decomposition selects discs and spheroids with less distinct properties. At these low masses, both the discs and spheroids have exponential profiles with high minor-to-major axes ratios, i.e. thickened discs.
Original language | English (US) |
---|---|
Pages (from-to) | 467-486 |
Number of pages | 20 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 459 |
Issue number | 1 |
DOIs | |
State | Published - Jun 11 2016 |
Keywords
- Galaxies: fundamental parameters
- Galaxies: kinematics and dynamics
- Galaxies: stellar content
- Galaxies: structure
- Methods: numerical
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science