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On the Robustness of the Velocity Anisotropy Parameter in Probing the Stellar Kinematics in Milky Way-Like Galaxies: Takeaway from TNG50 Simulation

Emami, Razieh and Hernquist, Lars and Vogelsberger, Mark and Shen, Xuejian and Speagle, Joshua S. and Moreno, Jorge and Alcock, Charles and Genel, Shy and Forbes, John C. and Marinacci, Federico and Torrey, Paul (2022) On the Robustness of the Velocity Anisotropy Parameter in Probing the Stellar Kinematics in Milky Way-Like Galaxies: Takeaway from TNG50 Simulation. Astrophysical Journal, 937 (1). p. 20. ISSN 0004-637X. doi:10.3847/1538-4357/ac86c7.

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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 (A-C) that show mild-to-strong sensitivity to different selections. The above classes cover 48%, 16%, and 36% of the halos, respectively. We analyze the β radial profiles and divide them into either monotonically increasing radial profiles or ones with peaks and troughs. We demonstrate that halos with monotonically increasing β profiles are mostly from class A, while those with peaks/troughs are part of classes B and 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 β energy space and compare that against the β radial profile. It is seen than 65% of halos with very mild sensitivity to different selections in real space are those for which the β radial and energy profiles are closely related. Consequently, we propose that comparing the β 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 β 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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Emami, Razieh0000-0002-2791-5011
Hernquist, Lars0000-0001-6950-1629
Vogelsberger, Mark0000-0001-8593-7692
Shen, Xuejian0000-0002-6196-823X
Speagle, Joshua S.0000-0003-2573-9832
Moreno, Jorge0000-0002-3430-3232
Alcock, Charles0000-0002-7892-3636
Genel, Shy0000-0002-3185-1540
Forbes, John C.0000-0002-1975-4449
Marinacci, Federico0000-0003-3816-7028
Torrey, Paul0000-0002-5653-0786
Additional Information:It is a great pleasure to thank Sirio Belli, Sownak Bose, Shep Doeleman, and Sandro Tacchella for very insightful conversations. R.E. acknowledges support by the Institute for Theory and Computation at the Center for Astrophysics. We thank the supercomputer facility at Harvard, where most of the simulation work was done. M.V. acknowledges support through an MIT RSC award, a Kavli Research Investment Fund, NASA ATP grant NNX17AG29G, and NSF grants AST-1814053, AST-1814259, and AST-1909831. F.M. acknowledges support through the Program "Rita Levi Montalcini" of the Italian MIUR. The TNG50 simulation was realized with computing time granted by the Gauss Center for Supercomputing (GCS) under GCS Large-Scale Projects GCS-DWAR on the GCS share of the supercomputer Hazel Hen at the High Performance Computing Center Stuttgart (HLRS).
Funding AgencyGrant Number
Harvard UniversityITC
Issue or Number:1
Record Number:CaltechAUTHORS:20220923-942198900.17
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117131
Deposited By: Melissa Ray
Deposited On:28 Sep 2022 21:47
Last Modified:28 Sep 2022 21:47

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