Identifying Kinematic Structures in Simulated Galaxies Using Unsupervised Machine Learning

Du, Min; Ho, Luis C.; Zhao, Dongyao; Shi, Jingjing; Debattista, Victor P.; Hernquist, Lars; Nelson, Dylan

doi:10.3847/1538-4357/ab43cc

Cited by 35 publications

(36 citation statements)

References 85 publications

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“…Improving upon that method, Obreja et al (2018) used Gaussian Mixture Models on dynamical parameters of galaxies from zoom-in simulation. Later, Du et al (2019) used the same method on unbarred disk-dominated galaxies of IllustrisTNG100, demonstrating that multiple galactic substructures can be found in large-volume simulations as well. Additionally, Brook et al (2012) studied the chemical composition and evolution of the bulge fraction over time in a zoom-in simulation.…”

Section: Introductionmentioning

confidence: 97%

Probabilistic model for dynamic galaxy decomposition

Jagvaral,

Campbell,

Mandelbaum

et al. 2021

Preprint

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In the era of precision cosmology and ever-improving cosmological simulations, a better understanding of different galaxy components such as bulges and discs will give us new insight into galactic formation and evolution. Based on the fact that the stellar populations of the constituent components of galaxies differ by their dynamical properties, we develop two simple models for galaxy decomposition using the IllustrisTNG cosmological hydrodynamical simulation. The first model uses a single dynamical parameter and can distinguish 4 components: thin disc, thick disc, counter-rotating disc and bulge. The second model uses one more dynamical parameter, was defined in a probabilistic manner, and distinguishes two components: bulge and disc. The number fraction of disc-dominated galaxies at a given stellar mass obtained by our models agrees well with observations for masses exceeding log 10 (𝑀 * /𝑀 ) = 10. Sérsic indices and half-mass radii for the bulge components agree well with those for real galaxies. The mode of the distribution of Sérsic indices for the disc components is at the expected value of 𝑛 = 1. However, disc half-mass radii are smaller than those for real galaxies, in accordance with previous findings that the IllustrisTNG simulation produces undersized discs.

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Section: Introductionmentioning

confidence: 97%

Probabilistic model for dynamic galaxy decomposition

Jagvaral,

Campbell,

Mandelbaum

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…From a numerical perspective, recent and current cosmological hydrodynamical simulation projects, such as IllustrisTNG 1 and EAGLE 2 , have been able to reproduce large numbers of galaxies across the morphological spectrum with well-resolved structures (Pillepich et al 2019;Pulsoni et al 2020;Rodriguez-Gomez et al 2019;Du et al 2019;Correa et al 2017). Structures like Gaia-Enceladus in the Galactic inner stellar halo also arise in Milky Way-like simulated galaxies (e.g.…”

Section: Introductionmentioning

confidence: 99%

The Fornax3D project: discovery of ancient massive merger events in the Fornax cluster galaxies NGC 1380 and NGC 1427

Zhu,

van de Ven,

Leaman

et al. 2022

Preprint

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We report the discovery of ancient massive merger events in the early-type galaxies NGC 1380 and NGC 1427 in the Fornax galaxy cluster. Both galaxies are observed by the MUSE IFU instrument on the VLT, as part of the Fornax3D project. By fitting recentlydeveloped population-orbital superposition models to the observed surface brightness as well as stellar kinematic, age, and metallicity maps, we obtain the stellar orbits, age and metallicity distributions of each galaxy. We then decompose each galaxy into multiple orbital-based components, including a dynamically hot inner stellar halo component which is identified as the relic of past massive mergers. By comparing to analogues from cosmological galaxy simulations, chiefly TNG50, we find that the formation of such a hot inner stellar halo requires the merger with a now-destroyed massive satellite galaxy of 3.7 +2.7 −1.5 × 10 10 M (about 1/5 of its current stellar mass) and of 1.5 +1.6 −0.7 × 10 10 M (about 1/4 of its current stellar mass) in the case of NGC 1380 and NGC 1427, respectively. Moreover, we infer that the last massive merger in NGC 1380 happened ∼ 10 Gyr ago based on the stellar age distribution of the re-grown dynamically cold disk, whereas the merger in NGC 1427 ended t 8 Gyr ago based on the stellar populations in its hot inner stellar halo. The major merger event in NGC 1380 is the first one with both merger mass and merger time quantitatively inferred in a galaxy beyond the Local Volume. Moreover, it is the oldest and most massive one uncovered in nearby galaxies so far.

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“…We identify kinematic structures in galaxies from TNG50 with the framework introduced in Du et al (2019Du et al ( , 2020. We here give only a brief overview of the method: all that follows applied exclusively to the stellar component of gaalxies.…”

Section: Extracting Kinematic Structures: Methodologymentioning

confidence: 99%

“…Understanding the evolution of galaxies in numerical simulations is required to help recovering the comparable evolution of real galaxies. As a first step in this process, we developed a fully automatic Gaussian mixture model, called auto-GMM that can decompose simulated galaxies in a non-parametric, accurate, and efficient way (Du et al 2019). This method takes full use of the 6D information of the position and velocity for every star (i.e.…”

Section: Introductionmentioning

confidence: 99%

The Evolutionary Pathways of Disk-, Bulge-, and Halo-dominated Galaxies

Du,

Ho,

Debattista

et al. 2021

Preprint

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We have recently developed a method to kinematically decompose simulated galaxies that helps to break the degeneracy among galactic stellar structures. For example, the concept of stellar halos is generalized to weakly-rotating structures that are composed of loosely bound stars, which can hence be associated to both disk and elliptical type morphologies. By applying this method to about 500 central galaxies with stellar mass 10 10−11.5 M from the TNG50 simulation at z = 0, we identify three broadly-defined types of galaxies: ones dominated by disk, by bulge, or by stellar halo structures. We then use the simulation to infer the underlying connection between the growth of structures and physical processes over cosmic time. Tracing galaxies back in time, we recognize three fundamental regimes: an early phase of evolution (z 2), and internal and external (mainly mergers) processes that act at later times. We find that disk-and bulge-dominated galaxies are not significantly affected by mergers since z ∼ 2; the difference in their presentday structures originates from two distinct evolutionary pathways, extended vs. compact, that are likely determined by their parent dark matter halos in the early phase; i.e., nature. On the other hand, normal elliptical galaxies are typically halo-dominated, forming by external processes (e.g. major mergers) in the later phase, i.e., nurture. This picture challenges the general idea that elliptical galaxies are the same objects as classical bulges in disk galaxies. In observations, both bulge-and halo-dominated galaxies are likely to be classified as early-type galaxies with compact morphology and quiescent star formation. However, here we find them to have very different evolutionary histories.

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Identifying Kinematic Structures in Simulated Galaxies Using Unsupervised Machine Learning

Cited by 35 publications

References 85 publications

Probabilistic model for dynamic galaxy decomposition

Probabilistic model for dynamic galaxy decomposition

The Fornax3D project: discovery of ancient massive merger events in the Fornax cluster galaxies NGC 1380 and NGC 1427

The Evolutionary Pathways of Disk-, Bulge-, and Halo-dominated Galaxies

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