The metallicity distribution in the core of the Sagittarius dwarf spheroidal: Minimising the metallicity biases

Minelli, A.; Bellazzini, M.; Mucciarelli, A.; Bonifacio, P.; Ibata, Rodrigo; Romano, D.; Monaco, L.; Caffau, E.; Dalessandro, E.; Pascale, Raffaele

doi:10.1051/0004-6361/202244890

Cited by 7 publications

(2 citation statements)

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“…We further notice that the locations of these metallicity peaks for both arms of the stream are well aligned with the secondary, more metal-poor, [Fe/H] peak for stars in the core of Sgr (grayish histograms in Figure 3; Hayes et al 2020/APOGEE 17 andMinelli et al 2023). Although differences in metallicity scales might be at play, this observation could be relevant for the evolution of the Sgr system in the presence of the Milky Way and LMC.…”

Section: Leading and Trailing Armssupporting

confidence: 58%

Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ([Fe/H] ≲ −3) Regime

Limberg

Queiroz

Perottoni

et al. 2023

ApJ

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In this work, we study the phase-space and chemical properties of the Sagittarius (Sgr) stream, the tidal tails produced by the ongoing destruction of the Sgr dwarf spheroidal (dSph) galaxy, focusing on its very metal-poor (VMP; [Fe/H] < −2) content. We combine spectroscopic and astrometric information from SEGUE and Gaia EDR3, respectively, with data products from a new large-scale run of the StarHorse spectrophotometric code. Our selection criteria yield ∼1600 stream members, including >200 VMP stars. We find the leading arm (b > 0°) of the Sgr stream to be more metal-poor, by ∼0.2 dex, than the trailing one (b < 0°). With a subsample of turnoff and subgiant stars, we estimate this substructure’s stellar population to be ∼1 Gyr older than the thick disk’s. With the aid of an N-body model of the Sgr system, we verify that simulated particles stripped earlier (>2 Gyr ago) have present-day phase-space properties similar to lower metallicity stream stars. Conversely, those stripped more recently (<2 Gyr) are preferentially akin to metal-rich ([Fe/H] > −1) members of the stream. Such correlation between kinematics and chemistry can be explained by the existence of a dynamically hotter, less centrally concentrated, and more metal-poor population in Sgr dSph prior to its disruption, implying that this galaxy was able to develop a metallicity gradient before its accretion. Finally, we identified several carbon-enhanced metal-poor ([C/Fe] > +0.7 and [Fe/H] ≤ −1.5) stars in the Sgr stream, which might be in tension with current observations of its remaining core where such objects are not found.

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Section: Leading and Trailing Armssupporting

confidence: 58%

Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ([Fe/H] ≲ −3) Regime

Limberg

Queiroz

Perottoni

et al. 2023

ApJ

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“…As samples grew, chemical differences along the different arms of the stream were observed (e.g., Keller et al 2010;Carlin et al 2012Carlin et al , 2018Shi et al 2012;Hyde et al 2015;Hasselquist et al 2019;Yang et al 2019;Hayes et al 2020;Zhao et al 2020;Ramos et al 2022). Several studies have argued that there is a metallicity gradient in the core (e.g., Majewski et al 2013;Mucciarelli et al 2017;Vitali et al 2022;Minelli et al 2023). Other works have argued in favor of an initial metallicity gradient based on the radial velocity dispersions of stream stars in different metallicity bins (e.g., Gibbons et al 2017;Johnson et al 2020;Limberg et al 2023).…”

Section: Introductionmentioning

confidence: 99%

Chemical Cartography of the Sagittarius Stream with Gaia

Cunningham,

Hunt,

Price-Whelan

et al. 2024

ApJ

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The stellar stream connected to the Sagittarius (Sgr) dwarf galaxy is the most massive tidal stream that has been mapped in the Galaxy, and is the dominant contributor to the outer stellar halo of the Milky Way (MW). We present metallicity maps of the Sgr stream, using 34,240 red giant branch stars with inferred metallicities from Gaia BP/RP spectra. This sample is larger than previous samples of Sgr stream members with chemical abundances by an order of magnitude. We measure metallicity gradients with respect to Sgr stream coordinates (Λ, B), and highlight the gradient in metallicity with respect to stream latitude coordinate B, which has not been observed before. Including the core, we find ∇[M/H] = −2.48 ± 0.08 × 10−2 dex deg−1 above the stream track (B > B 0, where B 0 = 1.5° is the latitude of the Sgr remnant) and ∇[M/H] = −2.02 ± 0.08 × 10−2 dex deg−1 below the stream track (B < B 0). By painting metallicity gradients onto a tailored N-body simulation of the Sgr stream, we find that the observed metallicities in the stream are consistent with an initial radial metallicity gradient in the Sgr dwarf galaxy of ∼−0.1 to −0.2 dex kpc−1, well within the range of observed metallicity gradients in Local Group dwarf galaxies. Our results provide novel observational constraints for the internal structure of the dwarf galaxy progenitor of the Sgr stream. Leveraging new large data sets in conjunction with tailored simulations, we can connect the present-day properties of disrupted dwarfs in the MW to their initial conditions.

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The age, kinematics, and metallicity of nearby Sun-like stars and the history of the Milky Way disc

Gondoin¹

2023

A&A

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Contact. Investigating how the Milky Way formed and has evolved is an important topic in astrophysics that requires the determination of precise ages for large samples of stars over long periods. Aims. The present study addresses the formation history of nearby Sun-like stars using the emission reversal in the cores of their Ca II H&K Fraunhofer lines as an age indicator. Methods. I used an empirical age–activity relationship derived from stellar rotation period measurements in intermediate-age open clusters to infer the age distribution of a representative sample of nearby 0.85−1.0 M⊙ stars with −0.2 ≤ [Fe/H] ≤ +0.2. The evolution of the dispersion of their velocity components and of the mean iron abundance as a function of age is estimated. Results. The inferred age distribution shows a steep rise in star formation in the solar neighbourhood between 7 and 6 Gyr ago, with a maximum formation rate ∼5 Gyr ago. This rate then decays until ∼2 Gyr and rises again in the recent past. The dispersion of the radial and vertical velocity components of the sample stars is the largest at the time of maximum star formation. Their mean iron abundance first decays from a super-solar value ([Fe/H] ∼ +0.05) ∼ 6 Gyr ago to a sub-solar value ([Fe/H] ≤ −0.05) ∼ 4 Gyr ago and rises again in the recent past. Conclusions. This timeline is consistent with a scenario where the steep rise in the age distribution of nearby Sun-like stars around 7−6 Gyr is related to an external perturbation induced by a first close pericentric passage of the Sgr galaxy ∼6.5 Gyr ago. The Sgr galaxy would have been significantly stripped from its gas in this first encounter, thus explaining the weaker star formation during a more recent encounter ∼2 Gyr ago. The gas infall from the satellite galaxy onto the MilkyWay disc would have diluted its metallicity over an extended period of time after the first encounter. The turbulence induced in this initial encounter may be partly responsible for the increased dispersion of velocity components of the stars born around the age of maximum star formation. A continuous metal enrichment of the disc would have progressively compensated the decaying infall of low-metallicity gas leading to an increase in the mean stellar metallicity in the last 4 Gyr.

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The metallicity distribution in the core of the Sagittarius dwarf spheroidal: Minimising the metallicity biases

Cited by 7 publications

References 84 publications

Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ([Fe/H] ≲ −3) Regime

Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ([Fe/H] ≲ −3) Regime

Chemical Cartography of the Sagittarius Stream with Gaia

The age, kinematics, and metallicity of nearby Sun-like stars and the history of the Milky Way disc

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