The Poor Old Heart of the Milky Way

Rix, Hans─Walter; Chandra, Vedant; Andrae, R.; Price-Whelan, Adrian M.; Weinberg, David H.; Conroy, Charlie; Fouesneau, M.; Hogg, David W.; Angeli, F. De; Naidu, Rohan P.; Xiang, Maosheng; Ruz-Mieres, Daniela

doi:10.3847/1538-4357/ac9e01

Cited by 60 publications

(72 citation statements)

References 95 publications

(157 reference statements)

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“…Theoretically, our intrinsic scatter measurements provide a target for simulations of galaxy formation that have the resolution to track enrichment and feedback at the individual supernova level and ISM mixing processes at the 10 3 -10 4 M e mass scale. Chemodynamical studies show that the metallicity range spanned by our sample is one over which the Milky Way transitioned from disordered kinematics to a rotationally supported system (Belokurov & Kravtsov 2022;Conroy et al 2022;Rix et al 2022). The detailed abundance patterns of stars across this transition, including the individual element scatter about average trends, will help to reveal how today's Galactic disk emerged from the chaotic environment of the proto-Galaxy.…”

Section: Discussionmentioning

confidence: 89%

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

Griffith

Johnson

Weinberg

et al. 2023

ApJ

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We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (−2 ≲ [Fe/H] ≲ −1) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (<0.05 dex for all elements), we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H], the rms intrinsic scatter in [X/Fe] ranges from 0.04 (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [α/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is N ∼ 50. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass ∼6 × 104 M ⊙ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.

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Section: Discussionmentioning

confidence: 89%

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

Griffith

Johnson

Weinberg

et al. 2023

ApJ

Self Cite

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“…Recently, Myeong et al (2022) argued for an in situ origin of Heracles. More recently, this population has been interpreted as the first stars that formed in the MW, based on Gaia, APOGEE DR17, and H3 survey data (Belokurov & Kravtsov 2022;Conroy et al 2022;Rix et al 2022).…”

Section: Comparison With Other Scenariosmentioning

confidence: 99%

The Imprint of Clump Formation at High Redshift. II. The Chemistry of the Bulge

Debattista

Liddicott

Gonzalez

et al. 2023

ApJ

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In Paper I, we showed that clumps in high-redshift galaxies, having a high star formation rate density (ΣSFR), produce disks with two tracks in the [Fe/H]–[α/Fe] chemical space, similar to that of the Milky Way’s (MW’s) thin+thick disks. Here we investigate the effect of clumps on the bulge’s chemistry. The chemistry of the MW’s bulge is comprised of a single track with two density peaks separated by a trough. We show that the bulge chemistry of an N-body + smoothed particle hydrodynamics clumpy simulation also has a single track. Star formation within the bulge is itself in the high-ΣSFR clumpy mode, which ensures that the bulge’s chemical track follows that of the thick disk at low [Fe/H] and then extends to high [Fe/H], where it peaks. The peak at low metallicity instead is comprised of a mixture of in situ stars and stars accreted via clumps. As a result, the trough between the peaks occurs at the end of the thick disk track. We find that the high-metallicity peak dominates near the mid-plane and declines in relative importance with height, as in the MW. The bulge is already rapidly rotating by the end of the clump epoch, with higher rotation at low [α/Fe]. Thus clumpy star formation is able to simultaneously explain the chemodynamic trends of the MW’s bulge, thin+thick disks, and the splash.

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“…The spectra are provided for ∼ 220 million stars in Gaia with 𝐺 < 17.65. Despite their low resolution, several studies have demonstrated that the information content is sufficient to measure bulk spectroscopic parameters (𝑇 eff , log 𝑔, [M/H], Liu et al 2012;Witten et al 2022;Xylakis-Dornbusch et al 2022;Andrae et al 2022;Fouesneau et al 2022;Creevey et al 2022;Belokurov et al 2022;Rix et al 2022) although detailed chemical abundances are likely too challenging (Gavel et al 2021). However, particularly in cooler stars, the presence of molecular features in these spectra is detectable (Lucey et al 2022) enabling more accurate metallicity determinations and detailed carbon abundances.…”

Section: Unsupervised Classification Of O-rich/c-rich Long-period Var...mentioning

confidence: 99%

Hunting for C-rich long-period variable stars in the Milky Way's bar-bulge using unsupervised classification of Gaia BP/RP spectra

Sanders¹,

Matsunaga²

2023

Preprint

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The separation of oxygen-and carbon-rich AGB sources is crucial for their accurate use as local and cosmological distance and age/metallicity indicators. We investigate the use of unsupervised learning algorithms for classifying the chemistry of long-period variables from Gaia DR3's BP/RP spectra. Even in the presence of significant interstellar dust, the spectra separate into two groups attributable to O-rich and C-rich sources. Given these classifications, we utilise a supervised approach to separate O-rich and C-rich sources without BP/RP spectra but instead given broadband optical and infrared photometry finding a purity of our C-rich classifications of around 95 per cent. We test and validate the classifications against other advocated colour-colour separations based on photometry. Furthermore, we demonstrate the potential of BP/RP spectra for finding S-type stars or those possibly symbiotic sources with strong emission lines. Although our classification suggests the Galactic bar-bulge is host to very few C-rich long-period variable stars, we do find a small fraction of C-rich stars with periods > 250 day that are spatially and kinematically consistent with bar-bulge membership. We argue the combination of the observed number, the spatial alignment, the kinematics and the period distribution disfavour young metal-poor star formation scenarios either in situ or in an accreted host, and instead, these stars are highly likely to be the result of binary evolution and the evolved versions of blue straggler stars already observed in the bar-bulge.

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The Poor Old Heart of the Milky Way

Cited by 60 publications

References 95 publications

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

The Imprint of Clump Formation at High Redshift. II. The Chemistry of the Bulge

Hunting for C-rich long-period variable stars in the Milky Way's bar-bulge using unsupervised classification of Gaia BP/RP spectra

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