Accelerated phase-mixing in the stellar halo due to a rotating bar

Y., Davies, Elliot; M., Dillamore, Adam; Vasiliev, Eugene; Belokurov, Vasily

doi:10.1093/mnrasl/slad017

Cited by 5 publications

(9 citation statements)

References 32 publications

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“…However, since the stars interested in this work mainly belong to halo population with long orbital periods, the self-gravity could play an important role in shaping the characteristics of the chevron-like structures. This is consistent with the comparison between our simulation and the result from Davies et al (2023a), which shows more blurring chevron structures compared with our simulations. As a conclusion, a more realistic bar model including the decrease of pattern speed together with the selfgravity of the system should be considered in the future to investigate the chevron-like features in the Galaxy.…”

Section: Influence Of a Steadily Rotating Barsupporting

confidence: 93%

“…The peak values N of the chevron 4, 5, 6 are 1.5, 2.9, 1.6 × 10 4 in Figure 2, while these values fall below 1.2 × 10 4 in a bar-added nonaxisymmetric potential. Our results are consistent with Davies et al (2023a) that a rotating bar would result in a blurry chevron at r gc > 20 kpc.…”

Section: Influence Of a Steadily Rotating Barsupporting

confidence: 92%

“…The most significant difference is the chevron 2 (r apo ∼ 12.75 kpc), which is obvious in the subsample with small pericenter but almost invisible in the subsample with large pericenter. Davies et al (2023a) found that all the chevrons discovered in the Gaia RVS sample almost disappear when they only considered stars with large pericenter (r peri > 2 kpc). They thought it is somewhat in conflict with the smoothing effect of the bar in simulations, and suspected that a resonance effect may account for the formation of these chevrons.…”

Section: Influence Of a Steadily Rotating Barmentioning

confidence: 98%

“…The barlike perturbations is possibly related to the creation and growth of several substructures, such as Hyades, Sirius, Hercules, and Ophiuchus streams (Dehnen 1998;Antoja et al 2014;Hattori et al 2016Hattori et al , 2019. A recent simulation work of Davies et al (2023a) showed that a rotating bar could accelerate the phase mixing of these chevron-like substructures found in Belokurov et al (2023).…”

Section: Influence Of a Steadily Rotating Barmentioning

confidence: 99%

“…Motivated by Davies et al (2023a), we divide the K giant sample into two subsamples of large (r peri > R b , 1648 stars) and small (r peri < R b , 4301 stars) pericenter, where R b = 1.87 kpc is the bar scale length. Stars with a smaller pericenter are more likely to be strongly influenced by the bar.…”

Section: Influence Of a Steadily Rotating Barmentioning

confidence: 99%

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Detection of Multiple Phase Space Overdensities of GSE Stars by Orbit Integration

Zhao

Chang

et al. 2023

ApJ

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In N-body simulations, nearly radial mergers can form shell-like overdensities in the sky position and phase space (r − v r ) due to the combination of dynamical friction and tidal stripping. The merger event of Gaia-Sausage-Enceladus (GSE) has provided a unique opportunity to study the shells in the phase space. To search for them, we integrate the orbits of 5949 GSE-related halo K giants from the LAMOST survey and record their positions at all time intervals in the r − v r diagram. After the subtraction of a smoothed background, we find six significant and complete thin chevron-like overdensities. The apocenters r apo of stars in the six chevrons are around 6.75, 12.75, 18.75, 25.25, 27.25, and 30.25 kpc. These chevrons reveal the multiple pileups of GSE stars at different apocenters. The application of a different Milky Way mass M vir will change the opening angles of these chevrons, while leaving their apocenters almost unchanged. By comparing with a recent study of the phase space overdensities of local halo stars from the Gaia Radial Velocity Spectrometer survey, our results are more inclined to a medium M vir of 1012 M ⊙. The application of a nonaxisymmetric Galactic potential with a steadily rotating bar has a blurring effect on the appearance of these chevron-like overdensities, especially for the chevrons with r apo > 20 kpc.

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Section: Influence Of a Steadily Rotating Barsupporting

confidence: 93%

Section: Influence Of a Steadily Rotating Barsupporting

confidence: 92%

Section: Influence Of a Steadily Rotating Barmentioning

confidence: 98%

Section: Influence Of a Steadily Rotating Barmentioning

confidence: 99%

Section: Influence Of a Steadily Rotating Barmentioning

confidence: 99%

See 3 more Smart Citations

Detection of Multiple Phase Space Overdensities of GSE Stars by Orbit Integration

Zhao

Chang

et al. 2023

ApJ

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Stellar halo substructure generated by bar resonances

Belokurov

Evans

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Using data from the Gaia satellite’s Radial Velocity Spectrometer Data Release 3 (RVS, DR3), we find a new and robust feature in the phase space distribution of halo stars. It is a prominent ridge at constant energy and with angular momentum Lz > 0. We run test particle simulations of a stellar halo-like distribution of particles in a realistic Milky Way potential with a rotating bar. We observe similar structures generated in the simulations from the trapping of particles in resonances with the bar, particularly at the corotation resonance. Many of the orbits trapped at the resonances are halo-like, with large vertical excursions from the disc. The location of the observed structure in energy space is consistent with a bar pattern speed in the range Ωb ≈ 35 − 40 km s−1 kpc−1. Overall, the effect of the resonances is to give the inner stellar halo a mild, net spin in the direction of the bar’s rotation. As the distribution of the angular momentum becomes asymmetric, a population of stars with positive mean Lz and low vertical action is created. The variation of the average rotational velocity of the simulated stellar halo with radius is similar to the behaviour of metal-poor stars in data from the APOGEE survey. Though the effects of bar resonances have long been known in the Galactic disc, this is strong evidence that the bar can drive changes even in the diffuse and extended stellar halo through its resonances.

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The debris of the ‘last major merger’ is dynamically young

Donlon,

Newberg,

Sanderson

et al. 2024

Monthly Notices of the Royal Astronomical Society

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The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the ‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor collided with the MW proto-disk 8-11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the MW disk within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space, because the morphology of debris depends on how long it has had to phase mix. The recently-identified phase-space folds in Gaia DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago. We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data 1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’ did not collide with the MW proto-disk at early times, as is thought for the GSE, but instead collided with the MW disk within the last few Gyr, consistent with the body of work surrounding the VRM.

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Accelerated phase-mixing in the stellar halo due to a rotating bar

Cited by 5 publications

References 32 publications

Detection of Multiple Phase Space Overdensities of GSE Stars by Orbit Integration

Detection of Multiple Phase Space Overdensities of GSE Stars by Orbit Integration

Stellar halo substructure generated by bar resonances

The debris of the ‘last major merger’ is dynamically young

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