Stellar substructures in the solar neighbourhood

Stonkutė, E.; Tautvaišienė, G.; Nordström, B.; Ženovienė, R.

doi:10.1051/0004-6361/201321437

Cited by 7 publications

(3 citation statements)

References 53 publications

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“…Meanwhile, stars with higher metallicities formed and have stayed on (proper) thick disk-like orbits. This was not the original interpretation given by Helmi et al (2014) (and follow up papers such as Stonkutė et al 2012Stonkutė et al , 2013Stonkutė et al ,Ženovienė et al 2015 where the features were attributed to the presence of merger debris, whereas we now believe the latter is a minor contributor and what is seen is simply the imprint of an important transition in the history of the disk (similar conclusions using different orbital parameters were in fact reached earlier by Liu & van de Ven 2012).…”

Section: Further Insights On the Early Disk From Chemistry And Dynamicssupporting

confidence: 45%

Streams, Substructures, and the Early History of the Milky Way

Helmi

2020

Annu. Rev. Astron. Astrophys.

302

169

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The advent of the second data release of the Gaia mission, in combination with data from large spectroscopic surveys, is revolutionizing our understanding of the Galaxy. Thanks to these transformational data sets and the knowledge accumulated thus far, a new, more mature picture of the evolution of the early Milky Way is currently emerging. ▪ Two of the traditional Galactic components, namely, the stellar halo and the thick disk, appear to be intimately linked: Stars with halo-like kinematics originate in similar proportions from a heated (thick) disk and from a debris from a system named Gaia-Enceladus. Gaia-Enceladus was the last big merger event experienced by the Milky Way and was completed around 10 Gyr ago. The puffed-up stars now present in the halo as a consequence of the merger have thus exposed the existence of a disk component at z ∼ 1.8. This is likely related to the previously known metal-weak thick disk and may be traceable to metallicities [Fe/H] [Formula: see text] −4. As importantly, there is evidence that the merger with Gaia-Enceladus triggered star formation in the early Milky Way, plausibly leading to the appearance of the thick disk as we know it. ▪ Other merger events have been characterized better, and new ones have been uncovered. These include, for example, the Helmi streams, Sequoia, and Thamnos, which add to the list of those discovered in wide-field photometric surveys, such as the Sagittarius streams. Current knowledge of their progenitors’ properties, star formation, and chemical evolutionary histories is still incomplete. ▪ Debris from different objects shows different degrees of overlap in phase-space. This sometimes confusing situation can be improved by determining membership probabilities via quantitative statistical methods. A task for the next few years will be to use ongoing and planned spectroscopic surveys for chemical labeling and to disentangle events from one another using dimensions other than phase-space, metallicity, or [α/Fe]. ▪ These large surveys will also provide line-of-sight velocities missing for faint stars in Gaia releases and more accurate distance determinations for distant objects, which in combination with other surveys could also lead to more accurate age dating. The resulting samples of stars will cover a much wider volume of the Galaxy, allowing, for example, the linking of kinematic substructures found in the inner halo to spatial overdensities in the outer halo. ▪ All the results obtained so far are in line with the expectations of current cosmological models. Nonetheless, tailored hydrodynamical simulations to reproduce in detail the properties of the merger debris, as well as constrained cosmological simulations of the Milky Way, are needed. Such simulations will undoubtedly unravel more connections between the different Galactic components and their substructures, and will aid in pushing our knowledge of the assembly of the Milky Way to the earliest times. Expected final online publication date for the Annual Review of Astronomy, Volume 58 is August 18, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Section: Further Insights On the Early Disk From Chemistry And Dynamicssupporting

confidence: 45%

Streams, Substructures, and the Early History of the Milky Way

Helmi

2020

Annu. Rev. Astron. Astrophys.

302

169

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“…The kinematic groups identified by Helmi et al (2006) that are likely formed from the accretion of stars from satellites also support this notion, since they have been shown to consist of predominantly old stars (e.g. Stonkutė et al 2013;Ženovienė et al 2014). Recently, Casagrande et al (2015, submitted) used the combination of asteroseismology and spectroscopy to study the vertical age gradient in the Galactic disc.…”

Section: The Quiescent Milky Waymentioning

confidence: 79%

“…the Hercules stream; Bensby et al 2007). However, some could have extragalactic origins (Stonkutė et al 2012(Stonkutė et al , 2013Ženovienė et al 2014. The ages of the latter kinematic groups suggest they were accreted early on ( > ∼ 8 Gyr ago).…”

Section: Introductionmentioning

confidence: 99%

The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc★

Ruchti¹,

Read²,

Feltzing³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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According to our current cosmological model, galaxies like the Milky Way are expected to experience many mergers over their lifetimes. The most massive of the merging galaxies will be dragged towards the disc-plane, depositing stars and dark matter into an accreted disc structure. In this work, we utilize the chemo-dynamical template developed in Ruchti et al. to hunt for accreted stars. We apply the template to a sample of 4,675 stars in the third internal data release from the Gaia-ESO Spectroscopic Survey. We find a significant component of accreted halo stars, but find no evidence of an accreted disc component. This suggests that the Milky Way has had a rather quiescent merger history since its disc formed some 8-10 billion years ago and therefore possesses no significant dark matter disc.

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Kinematically Detected Halo Streams

Smith

2016

Tidal Streams in the Local Group and Beyond

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Clues to the origins and evolution of our Galaxy can be found in the kinematics of stars around us. Remnants of accreted satellite galaxies produce over- densities in velocity-space, which can remain coherent for much longer than spatial over-densities. This chapter reviews a number of studies that have hunted for these accretion relics, both in the nearby solar-neighborhood and the more-distant stellar halo. Many observational surveys have driven this field forwards, from early work with the Hipparcos mission, to contemporary surveys like RAVE & SDSS. This active field continues to flourish, providing many new discoveries, and will be revolutionised as the Gaia mission delivers precise proper motions for a billion stars in our Galaxy.Comment: 27 pages, 10 figures. Chapter from Springer ASSL Volume entitled "Tidal Streams in the Local Group and Beyond". Affluent readers may wish to purchase the full volume here: http://link.springer.com/book/10.1007/978-3-319-19336-

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Stellar substructures in the solar neighbourhood

Cited by 7 publications

References 53 publications

Streams, Substructures, and the Early History of the Milky Way

Streams, Substructures, and the Early History of the Milky Way

The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc★

Kinematically Detected Halo Streams

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