TY - JOUR
T1 - NIHAO VI. The hidden discs of simulated galaxies
AU - Obreja, Aura
AU - Stinson, Gregory S.
AU - Dutton, Aaron A.
AU - Macciò, Andrea V.
AU - Wang, Liang
AU - Kang, Xi
N1 - Funding Information:
The simulation codes used in this project were developed by a large team led by Tom Quinn and James Wadsley. Without their contributions, this project would have been impossible. The authors are grateful to Julianne Dalcanton, Hans-Walter Rix, Marie Martig, Remco van den Bosch, Ling Zhu, Peter Yoachim, Glenn van de Ven and Rosa Domínguez Tenreiro for useful conversations and comments. The simulations were performed on the THEO and HYDRA clusters of the Max-Planck-Institut für Astronomie at the Rechenzentrum in Garching. We greatly appreciate the contributions of these computing allocations. AVM, AAD and GSS acknowledge support from the Sonderforschungsbereich SFB 881 'The Milky Way System' (subproject A1) of the German Research Foundation (DFG). GSS acknowledges funding from the European Research Council under the European Union's Seventh Framework Programme (FP 7) ERC Grant Agreement n. [321035]. XK is supported by the NSFC (No.11333008) and the strategic priority research program of CAS (No. XDB09000000).
Publisher Copyright:
© 2016 The Authors.
PY - 2016/6/11
Y1 - 2016/6/11
N2 - 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.
AB - 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.
KW - Galaxies: fundamental parameters
KW - Galaxies: kinematics and dynamics
KW - Galaxies: stellar content
KW - Galaxies: structure
KW - Methods: numerical
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U2 - 10.1093/mnras/stw690
DO - 10.1093/mnras/stw690
M3 - Article
AN - SCOPUS:84969962404
SN - 0035-8711
VL - 459
SP - 467
EP - 486
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -