The chemical evolution of the dwarf spheroidal galaxy Sextans

Theler, Romaine; Jablonka, P.; Lucchesi, Romain; Lardo, C.; North, P.; Irwin, M. J.; Battaglia, G.; Hill, V.; Tolstoy, Eline; Venn, Kim A.; Helmi, Amina; Kaufer, A.; Primas, F.; Shetrone, Matthew

doi:10.1051/0004-6361/201937146

Cited by 28 publications

(36 citation statements)

References 90 publications

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“…Sextans seems to have a lower plateau value of [Mg/Fe] than other dwarf galaxies (cf., e.g., Fig. 2 of Aoki et al 2009;Shetrone et al 2001;Theler 2015;Theler et al 2020). This deficiency of Mg at low metallicities is less striking when including NLTE corrections (Fig.…”

Section: A Recap On Nuclear Formation Sites and Abundance Trendsmentioning

confidence: 96%

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Neutron-capture elements in dwarf galaxies

Reichert

Hansen

Hanke

et al. 2020

A&A

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Context. We present a large homogeneous set of stellar parameters and abundances across a broad range of metallicities, involving 13 classical dwarf spheroidal (dSph) and ultra-faint dSph (UFD) galaxies. In total, this study includes 380 stars in Fornax, Sagittarius, Sculptor, Sextans, Carina, Ursa Minor, Draco, Reticulum II, Bootes I, Ursa Major II, Leo I, Segue I, and Triangulum II. This sample represents the largest, homogeneous, high-resolution study of dSph galaxies to date. Aims. With our homogeneously derived catalog, we are able to search for similar and deviating trends across different galaxies. We investigate the mass dependence of the individual systems on the production of α-elements, but also try to shed light on the long-standing puzzle of the dominant production site of r-process elements. Methods. We used data from the Keck observatory archive and the ESO reduced archive to reanalyze stars from these 13 classical dSph and UFD galaxies. We automatized the step of obtaining stellar parameters, but ran a full spectrum synthesis (1D, local thermal equilibrium) to derive all abundances except for iron to which we applied nonlocal thermodynamic equilibrium corrections where possible. Results. The homogenized set of abundances yielded the unique possibility of deriving a relation between the onset of type Ia supernovae and the stellar mass of the galaxy. Furthermore, we derived a formula to estimate the evolution of α-elements. This reveals a universal relation of these systems across a large range in mass. Finally, we show that between stellar masses of 2.1 × 107 M⊙ and 2.9 × 105 M⊙, there is no dependence of the production of heavy r-process elements on the stellar mass of the galaxy. Conclusions. Placing all abundances consistently on the same scale is crucial to answering questions about the chemical history of galaxies. By homogeneously analyzing Ba and Eu in the 13 systems, we have traced the onset of the s-process and found it to increase with metallicity as a function of the galaxy’s stellar mass. Moreover, the r-process material correlates with the α-elements indicating some coproduction of these, which in turn would point toward rare core-collapse supernovae rather than binary neutron star mergers as a host for the r-process at low [Fe/H] in the investigated dSph systems.

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Section: A Recap On Nuclear Formation Sites and Abundance Trendsmentioning

confidence: 96%

“…Fig. 3.6 of Theler 2015; Theler et al 2020). For more information of the two of our most metal-poor stars in Sextans, we refer the reader to Lucchesi et al (2020).…”

Section: The Imf and The Alpha Kneementioning

confidence: 99%

Neutron-capture elements in dwarf galaxies

Reichert

Hansen

Hanke

et al. 2020

A&A

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“…The Milky Way, Gaia-Enceladus, and many of the surviving dwarf galaxies show similarly super-solar [α/Fe] at low metallicity. However, since the "knee" metallicity ([Fe/H] knee ) at which systems start to show decreasing [α/Fe] with metallicity is below [Fe/H] −1.8 in Fornax, Draco, Sculptor, and Sextans dwarf galaxies, they show lower [α/Fe] than Gaia-Enceladus or the Milky Way in-situ stars at [Fe/H] knee < [Fe/H] (Tolstoy et al 2009;Cohen & Huang 2009;Kirby et al 2011;Lemasle et al 2012Lemasle et al , 2014Hendricks et al 2014;Hill et al 2019;Theler et al 2020). Although the position of the knee is less clear in LMC, SMC, and Sagittarius, they also show low α-element abundance at [Fe/H] ∼ −1.5 (Nidever et al 2020;Hasselquist et al 2021).…”

Section: Chemical Enrichments In Sequoiamentioning

confidence: 99%

High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia

Matsuno,

Koppelman,

Helmi

et al. 2021

Preprint

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Context. Sequoia is a retrograde kinematic substructures in the nearby Galactic halo, whose properties are a matter of debate. For example, previous studies do not necessarily agree on the chemical abundances of Sequoia stars, which are important for understanding its nature. Aims. We characterize the chemical properties of a sample of stars from Sequoia by determining high-precision abundances. Methods. We measure abundances of Na, Mg, Si, Ti, Cr, Mn, Ni, Zn, Y, and Ba from a differential abundance analysis on high signal-to-noise ratio, high-resolution spectra from new observations and from archival data. We compare precisely-measured chemical abundances of 12 Sequoia candidates with those of typical halo stars from literature, which include also stars from Gaia-Enceladus. This allows us to characterize Sequoia and compare it to another Galactic building block. The comparison is made after putting all the abundances onto the same scale using standard stars. Results. There are significant difference in [Na/Fe], [Mg/Fe], [Ca/Fe], [Ti/Fe], [Zn/Fe], and [Y/Fe] between Sequoia and Gaia-Enceladus stars at −1.8 [Fe/H] −1.4 in the sense that these abundance ratios are lower in Sequoia. These differences are similar to those seen between Gaia-Enceladus and in-situ stars at higher metallicity, suggesting that Sequoia is affected by type Ia supernovae at lower metallicity than Gaia-Enceladus. We also confirm that the low [Mg/Fe] of Sequoia is seen in literature and in surveys, namely APOGEE DR16 and GALAH DR3, if the stars are kinematically selected in the same way. Conclusions. Sequoia stars have a distinct chemical abundance pattern and can be chemically separated from in-situ stars or Gaia-Enceladus stars if abundances are measured with sufficient precision, namely σ([X/Fe]) 0.07 dex.

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“…Ni and Co can also be produced by SNeIa (e.g., Travaglio et al 2005;Kirby et al 2018). However, the contribution by SNeIa starts to dominate the chemical evolution of the galaxy at higher metallicities ([Fe/H] ≥ -2; Theler et al 2020). The behavior of Ni/Fe in the low-metallicity range investigated here can therefore be attributed to Ni production by complete and incomplete Si burning.…”

Section: Iron-peak Elementsmentioning

confidence: 64%

“…However, their exact significance and their role in galaxy formation remain to be clarified. In particular, the abundance patterns in dSph stars differ drastically from those of the field Milky Way (MW) halo population above [Fe/H] ∼ −2 (Shetrone et al 2001a;Venn et al 2004;Tolstoy et al 2009;Letarte et al 2010;Jablonka et al 2015;Hill et al 2019;Theler et al 2020). Nonetheless, dwarf galaxies offer the most metal-poor galactic environments that can be investigated.…”

Section: Introductionmentioning

confidence: 99%

Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxy

Lucchesi

Lardo

Primas

et al. 2020

A&A

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We present the high-resolution spectroscopic analysis of two new extremely metal-poor star (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were preselected from medium-resolution spectra centered around the Ca II triplet in the near-infrared and were followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H] = −2.95 and [Fe/H] = −3.01, which place them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the α, Fe-peak, and neutron-capture elements, are determined. In particular, we present the first unambiguous detection of Zn in a classical dwarf at extremely low metallicity. Previous indications were made of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H] ∼ − 3 when compared to other galaxies, particularly with very low observed [α/Fe] ratios. We took the opportunity of reanalyzing the full sample of EMPS in Sextans and find a [α/Fe] Milky Way-like plateau and a ∼0.2 dex dispersion at fixed metallicity.

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The chemical evolution of the dwarf spheroidal galaxy Sextans

Cited by 28 publications

References 90 publications

Neutron-capture elements in dwarf galaxies

Neutron-capture elements in dwarf galaxies

High-precision chemical abundances of Galactic building blocks. The distinct chemical abundance sequence of Sequoia

Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxy

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