What is the Milky Way outer halo made of?

Battaglia, G.; North, P.; Jablonka, P.; Shetrone, M.; Minniti, D.; Díaz, Matías R.; Starkenburg, Else; Savoy, Michael R.

doi:10.1051/0004-6361/201731879

Cited by 18 publications

(13 citation statements)

References 140 publications

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“…We note that Milone et al (2020) did not find any significant differences in the multiple populations between star clusters associated with different progenitors (see also Saracino et al 2020). However, there has been a number of numerical and observational works attempting to describe the formation of globular clusters with multiple populations that are in very good agreement with some aspects of the intra-cluster Na enrichment scenario suggested in this work (see, e.g., Bekki 2006;Carretta et al 2010;Maxwell et al 2014;Battaglia et al 2017;Santistevan et al 2020).…”

Section: Analysis and Discussionsupporting

confidence: 75%

“…It has been shown that the most Na-poor limit in dwarf galaxies is lower than the Na abundance of Milky Way field stars, with some exceptions (Colucci et al 2012;Ishigaki et al 2014;Battaglia et al 2017;Villanova et al 2019;Salgado et al 2019;Matsuno et al 2019;Aguado et al 2020). Therefore, first generation stars of globular clusters formed in accreted dwarf galaxies should mostly have Na abundances lower than their counterparts of globular clusters that formed in situ, which explains the range of 1G values seen in Fig.…”

Section: Analysis and Discussionmentioning

confidence: 99%

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Different sodium enhancements among multiple populations of Milky Way globular clusters

Piatti

2020

A&A

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We searched for clues to understand the different Na abundances measured in first and second generation stars of ancient Milky Way globular clusters. For that purpose, from the recent literature, we gathered the aforementioned Na abundances, orbital parameters, and structural and internal dynamical properties and ages in a homogeneous scale of 28 globular clusters. We found that the intra-cluster Na enrichment, which is measured by the difference of Na abundances between first and second generation stars, exhibits a trend as a function of the Na abundances of first generation stars, in the sense that the more Na-poor the first generation stars are, the larger the Na enrichment is. By using the inclinations of the globular clusters’ orbits, the analyzed Na enrichments also hinted at a boundary at ∼0.3 dex to differentiate globular clusters with an accreted or in situ origin, the accreted globular clusters having larger Na enrichments. Because relatively larger intra-cluster Na enhancements are seen in accreted globular clusters and small Na enhancements are observed in globular clusters formed in situ, although not exclusively, we speculate that the amplitude of the Na enrichment may be linked with the building block paradigm. Globular clusters at the time of formation of first and second generation stars would seem to keep a memory of this hierarchical galaxy formation process.

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Section: Analysis and Discussionsupporting

confidence: 75%

Section: Analysis and Discussionmentioning

confidence: 99%

Different sodium enhancements among multiple populations of Milky Way globular clusters

Piatti

2020

A&A

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“…An external enrichment scenario is principally supported by the outer halo nature of HE 1327−2326 and similar metal-poor stars (Tissera et al 2014;Battaglia et al 2017). As such, they are likely accreted from some smaller now disrupted system, such as a primordial minihalo.…”

Section: Evidence For Aspherical Explosions From Rotationmentioning

confidence: 99%

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

Ezzeddine

Frebel

Roederer

et al. 2019

ApJ

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We present observational evidence that an aspherical supernova explosion could have occurred in the first stars in the early universe. Our results are based on the first determination of a Zn abundance in a Hubble Space Telescope/Cosmic Origins Spectrograph high-resolution UV spectrum of a hyper metalpoor (HMP) star, HE 1327−2326, with [Fe/H](NLTE) = −5.2. We determine [Zn/Fe] = 0.80 ± 0.25 from a UV Zn i line at 2138Å, detected at 3.4 σ. Yields of a 25 M aspherical supernova model with artificially modified densities exploding with E = 5 × 10 51 ergs best match the entire abundance pattern of HE 1327−2326. Such high-entropy hypernova explosions are expected to produce bipolar outflows which could facilitate the external enrichment of small neighboring galaxies. This has already been predicted by theoretical studies of the earliest star forming minihalos. Such a scenario would have significant implications for the chemical enrichment across the early universe as HMP Carbon Enhanced Metal-Poor (CEMP) stars such as HE 1327−2326 might have formed in such externally enriched environments.

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“…An abundance study of the distant halo stars is of course possible (see e.g. Battaglia et al 2017) but is always limited to giant stars at fainter apparent magnitudes thus making such an endeavour much more laborious.…”

Section: Introductionmentioning

confidence: 99%

The S2 Stream: the shreds of a primitive dwarf galaxy.*

Aguado

Belokurov

Evans

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The S2 stream is a kinematically cold stream that is plunging downwards through the Galactic disc. It may be part of a hotter and more diffuse structure called the Helmi stream. We present a multi-instrument chemical analysis of the stars in the metal-poor S2 stream using both high- and low-resolution spectroscopy, complemented with a re-analysis of the archival data to give a total sample of 62 S2 members. Our high-resolution program provides α-elements (C, Mg, Si, Ca and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-capture process elements (Sr, Ba) and other elements such as Li, Na, Al, and Sc for a subsample of S2 objects. We report coherent abundance patterns over a large metallicity spread (∼1 dex) confirming that the S2 stream was produced by a disrupted dwarf galaxy. The combination of S2’s α-elements displays a mildly decreasing trend with increasing metallicity which can be tentatively interpreted as a “knee” at [Fe/H]<−2. At the low metallicity end, the n-capture elements in S2 may be dominated by r-process production however several stars are Ba-enhanced, but unusually poor in Sr. Moreover, some of the low-[Fe/H] stars appear to be carbon-enhanced. We interpret the observed abundance patterns with the help of chemical evolution models that demonstrate the need for modest star-formation efficiency and low wind efficiency confirming that the progenitor of S2 was a primitive dwarf galaxy.

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What is the Milky Way outer halo made of?

Cited by 18 publications

References 140 publications

Different sodium enhancements among multiple populations of Milky Way globular clusters

Different sodium enhancements among multiple populations of Milky Way globular clusters

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

The S2 Stream: the shreds of a primitive dwarf galaxy.*

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What is the Milky Way outer halo made of?

Cited by 18 publications

References 140 publications

Different sodium enhancements among multiple populations of Milky Way globular clusters

Different sodium enhancements among multiple populations of Milky Way globular clusters

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326∗

The S2 Stream: the shreds of a primitive dwarf galaxy.*

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Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗