Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies?
We present spectroscopy of the ultra-faint Milky Way satellites Eridanus III (Eri III) and DELVE 1. We identify eight member stars in each satellite and place nonconstraining upper limits on their velocity and metallicity dispersions. The brightest star in each object is very metal poor, at [Fe/H] =...
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2024-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ad85dd |
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| author | Joshua D. Simon Ting S. Li Alexander P. Ji Andrew B. Pace Terese T. Hansen William Cerny Ivanna Escala Sergey E. Koposov Alex Drlica-Wagner Sidney Mau Evan N. Kirby |
| author_facet | Joshua D. Simon Ting S. Li Alexander P. Ji Andrew B. Pace Terese T. Hansen William Cerny Ivanna Escala Sergey E. Koposov Alex Drlica-Wagner Sidney Mau Evan N. Kirby |
| author_sort | Joshua D. Simon |
| collection | DOAJ |
| description | We present spectroscopy of the ultra-faint Milky Way satellites Eridanus III (Eri III) and DELVE 1. We identify eight member stars in each satellite and place nonconstraining upper limits on their velocity and metallicity dispersions. The brightest star in each object is very metal poor, at [Fe/H] = −3.1 for Eri III and [Fe/H] = −2.8 for DELVE 1. Both of these stars exhibit large overabundances of carbon and very low abundances of the neutron-capture elements Ba and Sr, and we classify them as CEMP-no stars. Because their metallicities are well below those of the Milky Way globular cluster population, and because no CEMP-no stars have been identified in globular clusters, these chemical abundances could suggest that Eri III and DELVE 1 are dwarf galaxies. On the other hand, the two systems have half-light radii of 8 pc and 6 pc, respectively, which are more compact than any known ultra-faint dwarfs. We conclude that Eri III and DELVE 1 are either the smallest dwarf galaxies yet discovered, or they are representatives of a new class of star clusters that underwent chemical evolution distinct from that of ordinary globular clusters. In the latter scenario, such objects are likely the most primordial star clusters surviving today. These possibilities can be distinguished by future measurements of carbon and/or iron abundances for larger samples of stars or improved stellar kinematics for the two systems. |
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| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2024-01-01 |
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| series | The Astrophysical Journal |
| spelling | doaj-art-a4d98e944fcf4645b7c1768a57e3b64f2024-11-27T05:13:11ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01976225610.3847/1538-4357/ad85ddEridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies?Joshua D. Simon0https://orcid.org/0000-0002-4733-4994Ting S. Li1https://orcid.org/0000-0002-9110-6163Alexander P. Ji2https://orcid.org/0000-0002-4863-8842Andrew B. Pace3https://orcid.org/0000-0002-6021-8760Terese T. Hansen4https://orcid.org/0000-0001-6154-8983William Cerny5https://orcid.org/0000-0003-1697-7062Ivanna Escala6https://orcid.org/0000-0002-9933-9551Sergey E. Koposov7https://orcid.org/0000-0003-2644-135XAlex Drlica-Wagner8https://orcid.org/0000-0001-8251-933XSidney Mau9https://orcid.org/0000-0003-3519-4004Evan N. Kirby10https://orcid.org/0000-0001-6196-5162Observatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USADepartment of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada; Dunlap Institute for Astronomy and Astrophysics, University of Toronto , 50 St George Street, Toronto, ON M5S 3H4, CanadaDepartment of Astronomy and Astrophysics, University of Chicago , 5640 S Ellis Avenue, Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USAMcWilliams Center for Cosmology, Carnegie Mellon University , 5000 Forbes Avenue, Pittsburgh, PA 15213, USADepartment of Astronomy, Stockholm University , AlbaNova University Center, SE-106 91 Stockholm, SwedenDepartment of Astronomy, Yale University , New Haven, CT 06520, USAObservatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USA; Department of Astrophysical Sciences, Princeton University , 4 Ivy Lane, Princeton, NJ 08544, USAInstitute for Astronomy, University of Edinburgh , Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK; Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA, UK; Kavli Institute for Cosmology, University of Cambridge , Madingley Road, Cambridge CB3 0HA, UKDepartment of Astronomy and Astrophysics, University of Chicago , 5640 S Ellis Avenue, Chicago, IL 60637, USA; Kavli Institute for Cosmological Physics, University of Chicago , Chicago, IL 60637, USA; Fermi National Accelerator Laboratory , P.O. Box 500, Batavia, IL 60510, USADepartment of Physics, Stanford University , 382 Via Pueblo Mall, Stanford, CA 94305, USA; Kavli Institute for Particle Astrophysics and Cosmology, P.O. Box 2450, Stanford University , Stanford, CA 94305, USADepartment of Physics and Astronomy, University of Notre Dame , 225 Nieuwland Science Hall, Notre Dame, IN 46556, USAWe present spectroscopy of the ultra-faint Milky Way satellites Eridanus III (Eri III) and DELVE 1. We identify eight member stars in each satellite and place nonconstraining upper limits on their velocity and metallicity dispersions. The brightest star in each object is very metal poor, at [Fe/H] = −3.1 for Eri III and [Fe/H] = −2.8 for DELVE 1. Both of these stars exhibit large overabundances of carbon and very low abundances of the neutron-capture elements Ba and Sr, and we classify them as CEMP-no stars. Because their metallicities are well below those of the Milky Way globular cluster population, and because no CEMP-no stars have been identified in globular clusters, these chemical abundances could suggest that Eri III and DELVE 1 are dwarf galaxies. On the other hand, the two systems have half-light radii of 8 pc and 6 pc, respectively, which are more compact than any known ultra-faint dwarfs. We conclude that Eri III and DELVE 1 are either the smallest dwarf galaxies yet discovered, or they are representatives of a new class of star clusters that underwent chemical evolution distinct from that of ordinary globular clusters. In the latter scenario, such objects are likely the most primordial star clusters surviving today. These possibilities can be distinguished by future measurements of carbon and/or iron abundances for larger samples of stars or improved stellar kinematics for the two systems.https://doi.org/10.3847/1538-4357/ad85ddCEMP starsDwarf galaxiesGalaxy chemical evolutionGlobular star clustersNucleosynthesisR-process |
| spellingShingle | Joshua D. Simon Ting S. Li Alexander P. Ji Andrew B. Pace Terese T. Hansen William Cerny Ivanna Escala Sergey E. Koposov Alex Drlica-Wagner Sidney Mau Evan N. Kirby Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies? The Astrophysical Journal CEMP stars Dwarf galaxies Galaxy chemical evolution Globular star clusters Nucleosynthesis R-process |
| title | Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies? |
| title_full | Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies? |
| title_fullStr | Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies? |
| title_full_unstemmed | Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies? |
| title_short | Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies? |
| title_sort | eridanus iii and delve 1 carbon rich primordial star clusters or the smallest dwarf galaxies |
| topic | CEMP stars Dwarf galaxies Galaxy chemical evolution Globular star clusters Nucleosynthesis R-process |
| url | https://doi.org/10.3847/1538-4357/ad85dd |
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