Stellar orbits in cosmological galaxy simulations: the connection to formation history and line-of-sight kinematics

Abstract

We analyze orbits of stars and dark matter out to three effective radii for 42 galaxies formed in cosmological zoom simulations. Box orbits always dominate at the centers and $z$-tubes become important at larger radii. We connect the orbital structure to the formation histories and specific features (e.g. disk, counter-rotating core, minor axis rotation) in two-dimensional kinematic maps. Globally, fast rotating galaxies with significant recent in situ star formation are dominated by $z$-tubes. Slow rotators with recent mergers have significant box orbit and $x$-tube components. Rotation, quantified by the ${\lambda }_R$-parameter often originates from streaming motion of stars on $z$-tubes but sometimes from figure rotation. The observed anti-correlation of $h_3$ and $V_0/\sigma$ in rotating galaxies can be connected to a dissipative formation history leading to high $z$-tube fractions. For galaxies with recent mergers in situ formed stars, accreted stars and dark matter particles populate similar orbits. Dark matter particles have isotropic velocity dispersions. Accreted stars are typically radially biased ($\beta \approx 0.2-0.4$). In situ stars become tangentially biased (as low as $\beta \approx -1.0$) if dissipation was relevant during the late assembly of the galaxy. We discuss the relevance of our analysis for integral field surveys and for constraining galaxy formation models.

21 pages, 19 figures

References in corpus (9)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• The SAURON project -- IX. A kinematic classification for early-type galaxies
• Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365
• The influence of gas on the structure of merger remnants
• Galaxy growth in the concordance $\Lambda$CDM cosmology
• The SAURON project - XII. Kinematic substructures in early-type galaxies: evidence for disks in fast rotators
• Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies
• Why stellar feedback promotes disc formation in simulated galaxies
• Dark matter content and internal dynamics of NGC 4697: NMAGIC particle models from slit data and planetary nebulae velocities

Cited by in corpus (15)

• The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics
• When the Jeans don't fit: How stellar feedback drives stellar kinematics and complicates dynamical modeling in low-mass galaxies
• The origin and properties of massive prolate galaxies in the Illustris simulation
• Integral-field kinematics and stellar populations of early-type galaxies out to three half-light radii
• The fate of the Antennae galaxies
• A discrete chemo-dynamical model of the giant elliptical galaxy NGC 5846: dark matter fraction, internal rotation and velocity anisotropy out to six effective radii
• SMART: A new implementation of Schwarzschild's Orbit Superposition technique for triaxial galaxies and its application to an N-body merger simulation
• The two phases of core formation -- orbital evolution in the centres of ellipticals with supermassive black hole binaries
• The SAMI Galaxy Survey: Environmental analysis of the orbital structures of passive galaxies
• Merger histories of brightest group galaxies from MUSE stellar kinematics
• Dynamical modelling of the twisted galaxy PGC 046832
• The Hector Survey: integral field spectroscopy of 100,000 galaxies
• A discrete chemo-dynamical model of M87's globular clusters: Kinematics extending to ~ 400 kpc
• Modeling Nearly Spherical Pure-Bulge Galaxies with a Stellar Mass-to-Light Ratio Gradient under the $\Lambda$CDM and MOND Paradigms: II. The Orbital Anisotropy of Slow Rotators within the Effective Radius
• Gurzadyan's Problem 5 and improvement of softenings for cosmological simulations using the PP method