Stellar substructures in the solar neighbourhood

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

doi:10.1051/0004-6361/201118760

Cited by 13 publications

(8 citation statements)

References 54 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: 46%

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: 46%

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

Helmi

2020

Annu. Rev. Astron. Astrophys.

302

169

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“…The sensitivity of oxygen, alpha, and Fe-peak element abundances to stellar atmospheric parameters were described in Stonkutė et al (2012). The sensitivity of the abundance estimates to changes in the atmospheric parameters by the assumed errors Δ[El/H] are illustrated for the star HD 224930 ( Table 2).…”

Section: Estimation Of Uncertaintiesmentioning

confidence: 99%

Stellar substructures in the solar neighbourhood

Stonkutė

Tautvaišienė

Nordström

et al. 2013

A&A

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Context. The evolution of chemical elements in a galaxy is linked to its star formation history. Variations in star formation history are imprinted in the relative abundances of chemical elements produced in different supernova events and asymptotic giant branch stars. Aims. We determine detailed elemental abundances of s-and r-process elements in stars belonging to Group 3 of the Geneva-Copenhagen survey and compare their chemical composition with Galactic disc stars. The aim is to look for possible chemical signatures that might give information about the formation history of this kinematic group of stars, which is suggested to correspond to remnants of disrupted satellites. Methods. High-resolution spectra were obtained with the FIES spectrograph at the Nordic Optical Telescope, La Palma, and were analysed with a differential model atmosphere method. Comparison stars were observed and analysed with the same method. Results. Abundances of chemical elements produced mainly by the s-process are similar to those in the Galactic thin-disc dwarfs of the same metallicity, while abundances of chemical elements produced predominantly by the r-process are overabundant. The similar elemental abundances are observed in Galactic thick-disc stars. Conclusions. The chemical composition together with the kinematic properties and ages of stars in Group 3 of the Geneva-Copenhagen survey support a gas-rich satellite merger scenario as the most likely explanation for the origin. The similar chemical composition of stars in Group 3 and the thick-disc stars might suggest that their formation histories are linked.

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“…H06 . We have performed a high-resolution follow-up study of 72 of these stars, and have supplemented this dataset with that of Stonkutė et al (2012 of 21 stars in the same overdensity. As we shall see below, a few subpopulations of stars with different dynamics and chemical abundances coexist in this region of Galactic (extended) phase-space.…”

Section: Introductionmentioning

confidence: 99%

More Pieces of the Puzzle: Chemistry and Substructures in the Galactic Thick Disk

Helmi

Williams

Freeman

et al. 2014

ApJ

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We present a study of the chemical abundances of Solar neighbourhood stars associated to dynamical structures in the Milky Way's (thick) disk. These stars were identified as overdensity in the eccentricity range 0.3 < ǫ < 0.5 in the Copenhagen-Geneva Survey by Helmi et al. (2006). We find that the stars with these dynamical characteristics do not constitute a homogeneous population. A relatively sharp transition in dynamical and chemical properties appears to occur at a metallicity of [Fe/H] ∼ −0.4. Stars with [Fe/H] > −0.4 have mostly lower eccentricities, smaller vertical velocity dispersions, are α-enhanced and define a rather narrow sequence in [α/Fe] vs [Fe/H], clearly distinct from that of the thin disk. Stars with [Fe/H] < −0.4 have a range of eccentricities, are hotter vertically, and depict a larger spread in [α/Fe]. We have also found tentative evidence of substructure possibly associated to the disruption of a metal-rich star cluster. The differences between these populations of stars is also present in e.g. [Zn/Fe], [Ni/Fe] and [SmII/Fe], suggesting a real physical distinction.

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Stellar substructures in the solar neighbourhood

Cited by 13 publications

References 54 publications

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

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

Stellar substructures in the solar neighbourhood

More Pieces of the Puzzle: Chemistry and Substructures in the Galactic Thick Disk

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