Signatures of star streams in the phase space distribution  of nearby
 halo stars

Dettbarn, C.; Fuchs, B.; Flynn, Chris; Williams, M.

doi:10.1051/0004-6361:20077463

Cited by 20 publications

(41 citation statements)

References 27 publications

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“…By comparing the observed distribution of stars in the L z − L ⊥ space with Monte Carlo simulations of smooth, non rotating stellar halos, the over-density found at (L z , L ⊥ ) (1000, 2000) kpc km s −1 was shown to be significant and was interpreted as evidence of an accreted stream, known as the "Helmi stream" after this discovery. Other studies have subsequently confirmed the presence of this overdensity in the L z − L ⊥ space, confirming its extra-galactic nature (Chiba & Beers 2000;Re Fiorentin et al 2005;Dettbarn et al 2007;Kepley et al 2007;Klement et al 2009;Smith et al 2009;Re Fiorentin et al 2015) and concluding that approximately 5% of the local stellar halo should be made of stars belonging to this stream. Apart from the Helmi stream, possible others have potentially been detected in the L z − L ⊥ plane (see, for example Kepley et al 2007;Smith et al 2009;Re Fiorentin et al 2015).…”

Section: On the L ⊥ -L Z Spacementioning

confidence: 63%

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

Jean-Baptiste

Matteo

Haywood

et al. 2017

A&A

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The ΛCDM cosmological scenario predicts that our Galaxy should contain hundreds of stellar streams in the solar vicinity, fossil relics of the merging history of the Milky Way and more generally of the hierarchical growth of galaxies. Because of the mixing time scales in the inner Galaxy, it has been claimed that these streams should be difficult to detect in configuration space but can still be identifiable in kinematic-related spaces like the energy/angular momenta spaces, E − L z and L ⊥ − L z , or spaces of orbital/velocity parameters. By means of high-resolution, dissipationless N-body simulations containing between 25 × 10 6 and 35 × 10 6 particles, we model the accretion of a series of up to four 1:10 mass ratio satellites then up to eight 1:100 satellites and search systematically for the signature of accretions in these spaces. The novelty of this work with respect to the majority of those already published is our analysis of fully consistent models, where both the satellite(s) and the Milky Way galaxy are "live" systems, which can react to the interaction and experience kinematical heating, tidal effects and dynamical friction (the latter, a process often neglected in previous studies). We find that, in agreement with previous works, all spaces are rich in substructures, but that, contrary to previous works, the origin of these substructures -accreted or in-situ -cannot be determined for the following reasons. In all spaces considered (1) each satellite provides the origin of several independent over-densities; (2) over-densities of multiple satellites overlap; (3) satellites of different masses can produce similar substructures; (4) the overlap between the in-situ and the accreted population is considerable everywhere; and (5) in-situ stars also form substructures in response to the satellite(s') accretion. These points are valid even if the search is restricted to kinematically-selected halo stars only. As we are now entering the "Gaia era", our results warn that extreme caution must be employed before interpreting over-densities in any of those spaces as evidence of relics of accreted satellites. Reconstructing the accretion history of our Galaxy will require a substantial amount of accurate spectroscopic data, that, complemented by the kinematic information, will possibly allow us to (chemically) identify accreted streams and measure their orbital properties.

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Section: On the L ⊥ -L Z Spacementioning

confidence: 63%

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

Jean-Baptiste

Matteo

Haywood

et al. 2017

A&A

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“…Finally, to calculate the energy, one needs the full 6D phase space information (r, v), which can be observed, plus the potential (r), which is desired, but not directly observable. Therefore, alternative "effective" integrals of motion have been proposed (Helmi et al 2006;Arifyanto and Fuchs 2006;Dettbarn et al 2007;Klement et al 2008Klement et al , 2009). The idea behind such approaches is to find parameters that characterize stellar orbits and can be easily expressed through the observables.…”

Section: Integrals Of Motion and Action-angle Variablesmentioning

confidence: 99%

Halo streams in the solar neighborhood

Klement

2010

Astron Astrophys Rev

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The phase-space structure of our Galaxy holds the key to understand and reconstruct its formation. The CDM model predicts a richly structured phase-space distribution of dark matter and (halo) stars, consisting of streams of particles torn from their progenitors during the process of hierarchical merging. While such streams quickly loose their spatial coherence in the process of phase mixing, the individual stars keep their common origin imprinted into their kinematic and chemical properties, allowing the recovery of the Galaxy's individual "building blocks". The field of Galactic Archeology has witnessed a dramatic boost over the last decade, thanks to the increasing quality and size of available data sets. This is especially true for the solar neighborhood, a volume of 1-2 kpc around the sun, where large scale surveys like SDSS/SEGUE continue to reveal the full 6D phase-space information of thousands of halo stars. In this review, I summarize the discoveries of stellar halo streams made so far and give a theoretical overview over the search strategies imployed. This article is intended as an introduction to researchers new to the field, but also as a reference illustrating the achievements made so far. I conclude that disentangling the individual fragments from which the Milky Way was built requires more precise data that will ultimately be delivered by the Gaia mission.

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“…Indeed, their prominence close to the Sun's position in velocity space without any vertical flow (e.g., Seabroke et al 2007) is not compatible with the hypothesis that they are the result of merger events with satellite galaxies. Such satellite debris have been identified in the solar neigbourhood (Helmi et al 2006;Arifyanto & Fuchs 2006;Dettbarn et al 2007), but contain much fewer stars and move with higher velocities.…”

Section: Introductionmentioning

confidence: 99%

On the age heterogeneity of the Pleiades, Hyades, and Sirius moving groups

Famaey¹,

Siebert

Jorissen³

2008

A&A

100

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Aims. We investigate the nature of the classical low-velocity structures in the local velocity field, i.e. the Pleiades, Hyades, and Sirius moving groups. After using a wavelet transform to locate them in velocity space, we study their relation with the open clusters kinematically associated with them. Methods. By directly comparing the location of moving group stars in parallax space to the isochrones of the embedded clusters, we check whether, within the observational errors on the parallax, all moving group stars could originate from the ongoing evaporation of the associated cluster. Results. We conclude that, in each moving group, the fraction of stars making up the velocity-space overdensity superimposed on the background is higher than the fraction of stars compatible with the isochrone of the associated cluster. These observations thus favour a dynamical (resonant) origin for the Pleiades, Hyades, and Sirius moving groups.

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Signatures of star streams in the phase space distribution of nearby halo stars

Cited by 20 publications

References 27 publications

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

On the kinematic detection of accreted streams in theGaiaera: a cautionary tale

Halo streams in the solar neighborhood

On the age heterogeneity of the Pleiades, Hyades, and Sirius moving groups

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