The Pristine Inner Galaxy Survey (PIGS) X. Probing the early chemical evolution of the Sagittarius dwarf galaxy with carbon abundances
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| Format: | Preprint |
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2024
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| _version_ | 1866910659246030848 |
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| author | Sestito, Federico Ardern-Arentsen, Anke Vitali, Sara Montelius, Martin Lucchesi, Romain Venn, Kim A. Martin, Nicolas F. Navarro, Julio F. Starkenburg, Else |
| author_facet | Sestito, Federico Ardern-Arentsen, Anke Vitali, Sara Montelius, Martin Lucchesi, Romain Venn, Kim A. Martin, Nicolas F. Navarro, Julio F. Starkenburg, Else |
| contents | We aim to constrain the chemo-dynamical properties of the Sagittarius (Sgr) dwarf galaxy using carbon abundances. Our sample from the \textit{Pristine} Inner Galaxy Survey (PIGS) includes $\sim 350$ metal-poor ([Fe/H]~$<-1.5$) stars in the main body of Sgr with good quality spectroscopic observations. Our metal-poor Sgr population has a larger velocity dispersion than metal-rich Sgr from the literature, which could be explained by outside-in star formation, extreme Galactic tidal perturbations and/or the presence of a metal-rich disc/bar $+$ a metal-poor halo. The average carbon abundance [C/Fe] in Sgr is similar to that of other classical dwarf galaxies (DGs) and consistently lower than in the Milky Way by $\sim0.2-0.3$~dex at low metallicity. The interstellar medium in DGs, including Sgr, may have retained yields from more energetic Population~III~and~II supernovae (SNe), thereby reducing the average [C/Fe]. Additionally, SNe~Ia, producing more Fe than C, would start to contribute at lower metallicity in DGs/Sgr than in the Galaxy. The presence of a [C/Fe] gradient for Sgr stars with [Fe/H]~$\gtrsim-2.0$ ($\sim 6.8\times 10^{-4}\ \rm{dex \ arcmin^{-1}}$) suggests that SNe~Ia contributed in the system at those metallicities, especially in its inner regions. There is a low frequency of carbon-enhanced metal-poor (CEMP) stars in our Sgr sample. At higher metallicity/carbon abundance (mostly CEMP-s) this may be due to photometric selection effects, but those are less likely to affect CEMP-no stars. We propose that, given the lower average [C/Fe] in DGs, using the same CEMP definition ([C/Fe]~$>+0.7$) as in the Galaxy under-predicts the number of CEMP stars in DGs, and for Sgr a cut at [C/Fe]$~\sim +0.35$ may be more appropriate, which brings the frequency of CEMP stars in agreement with that in the Galaxy. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2406_18636 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The Pristine Inner Galaxy Survey (PIGS) X. Probing the early chemical evolution of the Sagittarius dwarf galaxy with carbon abundances Sestito, Federico Ardern-Arentsen, Anke Vitali, Sara Montelius, Martin Lucchesi, Romain Venn, Kim A. Martin, Nicolas F. Navarro, Julio F. Starkenburg, Else Astrophysics of Galaxies Solar and Stellar Astrophysics We aim to constrain the chemo-dynamical properties of the Sagittarius (Sgr) dwarf galaxy using carbon abundances. Our sample from the \textit{Pristine} Inner Galaxy Survey (PIGS) includes $\sim 350$ metal-poor ([Fe/H]~$<-1.5$) stars in the main body of Sgr with good quality spectroscopic observations. Our metal-poor Sgr population has a larger velocity dispersion than metal-rich Sgr from the literature, which could be explained by outside-in star formation, extreme Galactic tidal perturbations and/or the presence of a metal-rich disc/bar $+$ a metal-poor halo. The average carbon abundance [C/Fe] in Sgr is similar to that of other classical dwarf galaxies (DGs) and consistently lower than in the Milky Way by $\sim0.2-0.3$~dex at low metallicity. The interstellar medium in DGs, including Sgr, may have retained yields from more energetic Population~III~and~II supernovae (SNe), thereby reducing the average [C/Fe]. Additionally, SNe~Ia, producing more Fe than C, would start to contribute at lower metallicity in DGs/Sgr than in the Galaxy. The presence of a [C/Fe] gradient for Sgr stars with [Fe/H]~$\gtrsim-2.0$ ($\sim 6.8\times 10^{-4}\ \rm{dex \ arcmin^{-1}}$) suggests that SNe~Ia contributed in the system at those metallicities, especially in its inner regions. There is a low frequency of carbon-enhanced metal-poor (CEMP) stars in our Sgr sample. At higher metallicity/carbon abundance (mostly CEMP-s) this may be due to photometric selection effects, but those are less likely to affect CEMP-no stars. We propose that, given the lower average [C/Fe] in DGs, using the same CEMP definition ([C/Fe]~$>+0.7$) as in the Galaxy under-predicts the number of CEMP stars in DGs, and for Sgr a cut at [C/Fe]$~\sim +0.35$ may be more appropriate, which brings the frequency of CEMP stars in agreement with that in the Galaxy. |
| title | The Pristine Inner Galaxy Survey (PIGS) X. Probing the early chemical evolution of the Sagittarius dwarf galaxy with carbon abundances |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2406.18636 |