Unraveling the Complexity of Dwarf Galaxy Dynamics: A Study of Binary Orbital Motions

Wang, Wenting; Zhu, Ling; Jing, Yipeng; Grand, Robert J. J.; Li, Zhaozhou; Fu, Xiaoting; Li, Lu; Han, Jiaxin; Li, Ting S.; Feng, Fabo; Frenk, Carlos

Abstract

We investigate the impact of binary orbital motions on the dynamical modeling of dwarf galaxies with intrinsic line-of-sight velocity dispersions ( σvr ) of 1–9 km s−1. Using dwarf galaxies from the auriga level-2 and level-3 simulations, we apply the Jeans Anisotropic Multi-Gaussian Expansion modeling to tracer stars before and after including binaries to recover the dynamical masses. The recovered total masses within the half-mass radius of tracers, M(< r half), are always inflated due to binary motions, with greater inflations occurring for smaller σvr . However, many dwarf galaxies experience central density deflated due to binary motions, with little dependence on σvr . This is due to the negative radial gradients in the velocity dispersion profiles, with the fractional inflation in σvr due to binaries more significant in outskirts. An extreme binary fraction of 70% can lead to central density deflation of up to 10%–20% at 3 km s−1 < σvr < 8 km s−1, with M( < r half) inflated by 4% at 9 km s−1 and up to 15% at 3 km s−1. A lower binary fraction of 36% leads to similar deflations, with the inflations decreasing to approximately 10% at 3 km s−1 and becoming statistically insignificant. The choice of binary orbit distribution models does not result in significant differences, and observational errors tend to slightly weaken the deflations in the recovered central density. Two observations separated by 1 yr to exclude binaries lead to almost zero inflations/deflations for a binary fraction of 36% over 3 km s−1 < σvr<9 km s−1. For σvr∼1 km s−1 to 3 km s−1, a binary fraction of 70% (36%) still results in 60% (30%) to 10% (1%) of inflations in M( < r half), even with two-epoch observation.

Citation

Wang, W., Zhu, L., Jing, Y., Grand, R. J. J., Li, Z., Fu, X., …Frenk, C. (2023). Unraveling the Complexity of Dwarf Galaxy Dynamics: A Study of Binary Orbital Motions. Astrophysical Journal, 956(2), Article 91. https://doi.org/10.3847/1538-4357/acf314

• Journal Article Type: Article
• Acceptance Date: Aug 21, 2023
• Online Publication Date: Oct 11, 2023
• Publication Date: Oct 1, 2023
• Deposit Date: Oct 17, 2023
• Publicly Available Date: Oct 17, 2023
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 956
• Issue: 2
• Article Number: 91
• DOI: https://doi.org/10.3847/1538-4357/acf314
• Keywords: Binary stars, Dark matter, Dwarf galaxies, Hydrodynamical simulations
• Public URL: https://durham-repository.worktribe.com/output/1797868