On the robustness of the velocity anisotropy parameter in probing the stellar kinematics in Milky Way like galaxies: Take away from TNG50 simulation

Abstract

We analyze the velocity anisotropy of stars in real and energy space for a sample of Milky Way-like galaxies in the TNG50 simulation. We employ different selection criteria, including spatial, kinematic and metallicity cuts, and make three halo classes ($\mathcal{A}$-$\mathcal{C}$) which show mild-to-strong sensitivity to different selections. The above classes cover 48%, 16% and 36% of halos, respectively. We analyze the $\beta$ radial profiles and divide them into either monotonically increasing radial profiles or ones with peaks and troughs. We demonstrate that halos with monotonically increasing $\beta$ profiles are mostly from class $\mathcal{A}$, whilst those with peaks/troughs are part of classes $\mathcal{B}$-$\mathcal{C}$. This means that care must be taken as the observationally reported peaks/troughs might be a consequence of different selection criteria. We infer the anisotropy parameter $\beta$ energy space and compare that against the $\beta$ radial profile. It is seen that 65% of halos with very mild sensitivity to different selections in real space, are those for which the $\beta$ radial and energy profiles are closely related. Consequently, we propose that comparing the $\beta$ radial and energy profiles might be a novel way to examine the sensitivity to different selection criteria and thus examining the robustness of the anisotropy parameter in tracing stellar kinematics. We compare simulated $\beta$ radial profiles against various observations and demonstrate that, in most cases, the model diversity is comparable with the error bars from different observations, meaning that the TNG50 models are in good overall agreement with observations.

21 pages, 16 figures, Accepted for publication in ApJ

References in corpus (16)

• The NumPy array: a structure for efficient numerical computation
• The Observed properties of Dark Matter on small spatial scales
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• The kinematic status and mass content of the Sculptor dwarf spheroidal galaxy
• Velocity Dispersion Profiles of Seven Dwarf Spheroidal Galaxies
• Kinematics of the stellar halo and the mass distribution of the Milky Way using BHB stars
• The mass and velocity anisotropy of the Carina, Fornax, Sculptor and Sextans dwarf spheroidal galaxies
• Stellar kinematics in the remote Leo II dwarf spheroidal galaxy -- Another brick in the wall
• The M31 Velocity Vector. I. Hubble Space Telescope Proper Motion Measurements
• Dwarf Galaxy Dark Matter Density Profiles Inferred from Stellar and Gas Kinematics
• Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos
• When the Jeans don't fit: How stellar feedback drives stellar kinematics and complicates dynamical modeling in low-mass galaxies
• The SAMI Galaxy Survey: stellar population gradients of central galaxies
• The diversity of the circumgalactic medium around z = 0 Milky Way-mass galaxies from the Auriga simulations
• Resolving the mass--anisotropy degeneracy of the spherically symmetric Jeans equation I: theoretical foundation
• Resolving the mass--anisotropy degeneracy of the spherically symmetric Jeans equation II: optimum smoothing and model validation

Cited by in corpus (5)

• Where are the extremely metal-poor stars in the Milky Way and Andromeda? Expectations from TNG50
• Galaxy formation with wave/fuzzy dark matter: The core-halo structure and the solitonic imprint
• Probing the spatial and velocity anisotropies in stellar halos from the Aquarius simulations
• The dynamical lineage of ultra-diffuse galaxies from TNG50-1
• Unravelling the role of merger histories in the population of In situ stars: linking IllustrisTNG cosmological simulation to H3 survey