Examinando por Autor "Jablonka P."

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    Extremely metal-poor stars in the Fornax and Carina dwarf spheroidal galaxies
    (EDP Sciences, 2024-09) Lucchesi R.; Jablonka P.; Skúladóttir Á.; Lardo C.; Mashonkina L.; Primas F.; Venn K.; Hill V.; Minniti D.
    We present our analysis of VLT/UVES and X-shooter observations of six very metal-poor stars, including four stars at [Fe/H] ≈ -3 in the Fornax and Carina dwarf spheroidal (dSph) galaxies. To date, this metallicity range in these two galaxies has not yet been investigated fully, or at all in some cases. The chemical abundances of 25 elements are presented, based on 1D and local thermodynamic equilibrium (LTE) model atmospheres. We discuss the different elemental groups, and find that α- and iron-peak elements in these two systems are generally in good agreement with the Milky Way halo at the same metallicity. Our analysis reveals that none of the six stars we studied exhibits carbon enhancement, which is noteworthy given the prevalence of carbon-enhanced metal-poor stars without s-process enhancement (CEMP-no) in the Galaxy at similarly low metallicities. Our compilation of literature data shows that the fraction of CEMP-no stars in dSph galaxies is significantly lower than in the Milky Way, and than in ultra-faint dwarf galaxies. Furthermore, we report the discovery of the lowest metallicity, [Fe/H] = -2.92, r-process rich (r-I) star in a dSph galaxy. This star, fnx-06-019, has [Eu/Fe] = +0.8, and also shows enhancement of La, Nd, and Dy, [X/Fe] > +0.5. Our new data in Carina and Fornax help populate the extremely low metallicity range in dSph galaxies, and add to the evidence of a low fraction of CEMP-no stars in these systems.
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    The GOGREEN survey: Post-infall environmental quenching fails to predict the observed age difference between quiescent field and cluster galaxies at z > 1
    (Oxford University Press, 2020-11) Webb K.; Balogh M.L.; Leja J.; van der Burg R.F.J.; Rudnick G.; Muzzin A.; Boak K.; Cerulo P.; Gilbank D.; Lidman C.; Old L.J.; Pintos-Castro I.; McGee S.; Shipley H.; Biviano A.; Chan J.C.C.; Cooper M.; de Lucia G.; Demarco R.; Forrest B.; Jablonka P.; Kukstas E.; McCarthy I.G.; McNab K.; Nantais J.; Noble A.; Poggianti B.; Reeves A.M.M.; Vulcani B.; Wilson G.; Yee H.K.C.; Zaritsky D.
    We study the star formation histories (SFHs) and mass-weighted ages of 331 UVJ-selected quiescent galaxies in 11 galaxy clusters and in the field at 1 < z < 1.5 from the Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) survey. We determine the SFHs of individual galaxies by simultaneously fitting rest-frame optical spectroscopy and broadband photometry to stellar population models. We confirm that the SFHs are consistent with more massive galaxies having on average earlier formation times. Comparing galaxies found in massive clusters with those in the field, we find galaxies with M∗ < 1011.3 M in the field have more extended SFHs. From the SFHs we calculate the mass-weighted ages, and compare age distributions of galaxies between the two environments, at fixed mass. We constrain the difference in mass-weighted ages between field and cluster galaxies to 0.31+0.51−0.33 Gyr, in the sense that cluster galaxies are older. We place this result in the context of two simple quenching models and show that neither environmental quenching based on time since infall (without pre-processing) nor a difference in formation times alone can reproduce both the average age difference and relative quenched fractions. This is distinctly different from local clusters, for which the majority of the quenched population is consistent with having been environmentally quenched upon infall. Our results suggest that quenched population in galaxy clusters at z > 1 has been driven by different physical processes than those at play at z = 0. © 2020 The Author(s)