The Rapid Formation of the Metal-poor Milky Way
Our understanding of the assembly timeline of the Milky Way has been transforming along with the dramatic increase in astrometric and spectroscopic data available over the past several years. Many substructures in chemo-dynamical space have been discovered and identified as the remnants of various g...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad968e |
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| author | Turner Woody Charlie Conroy Phillip Cargile Ana Bonaca Vedant Chandra Jiwon Jesse Han Benjamin D. Johnson Rohan P. Naidu Yuan-Sen Ting |
| author_facet | Turner Woody Charlie Conroy Phillip Cargile Ana Bonaca Vedant Chandra Jiwon Jesse Han Benjamin D. Johnson Rohan P. Naidu Yuan-Sen Ting |
| author_sort | Turner Woody |
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| description | Our understanding of the assembly timeline of the Milky Way has been transforming along with the dramatic increase in astrometric and spectroscopic data available over the past several years. Many substructures in chemo-dynamical space have been discovered and identified as the remnants of various galactic mergers. To investigate the timeline of these mergers, we select main-sequence turnoff and subgiant stars (MSTOs) from the H3 survey, finding members in seven metal-poor components of the halo: Gaia-Sausage/Enceladus (GSE), the Helmi Streams, Thamnos, Sequoia, Wukong/LMS-1, Arjuna, and I’itoi. We also select out a metal-poor in situ population to facilitate comparison to the evolution of the Milky Way itself at these early epochs. We fit individual isochrone ages to the MSTOs in each of these substructures and use the resulting age distributions to infer simple star formation histories (SFHs). For GSE, we resolve an extended SFH that truncates ≈10 Gyr ago, as well as a clear age–metallicity relation. From this age distribution and measured SFH we infer that GSE merged with the Milky Way at a time 9.5–10.2 Gyr ago, in agreement with previous estimates. We infer that the other mergers occurred at various times ranging from 9 to 13 Gyr ago, and that the metal-poor in situ Galaxy built up within only a few billion years. These results reinforce the emerging picture that both the disk and halo of the Milky Way experienced a rapid assembly. |
| format | Article |
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| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-4b1f9ba5d2f54503b9eeb2383460e03d2025-01-08T07:10:31ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01978215210.3847/1538-4357/ad968eThe Rapid Formation of the Metal-poor Milky WayTurner Woody0https://orcid.org/0000-0002-0721-6715Charlie Conroy1https://orcid.org/0000-0002-1590-8551Phillip Cargile2https://orcid.org/0000-0002-1617-8917Ana Bonaca3https://orcid.org/0000-0002-7846-9787Vedant Chandra4https://orcid.org/0000-0002-0572-8012Jiwon Jesse Han5https://orcid.org/0000-0002-6800-5778Benjamin D. Johnson6https://orcid.org/0000-0002-9280-7594Rohan P. Naidu7https://orcid.org/0000-0003-3997-5705Yuan-Sen Ting8https://orcid.org/0000-0001-5082-9536Center for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA ; turner.woody@cfa.harvard.eduCenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA ; turner.woody@cfa.harvard.eduCenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA ; turner.woody@cfa.harvard.eduThe Observatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101, USACenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA ; turner.woody@cfa.harvard.eduCenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA ; turner.woody@cfa.harvard.eduCenter for Astrophysics ∣ Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138, USA ; turner.woody@cfa.harvard.eduMIT Kavli Institute for Astrophysics and Space Research , 77 Massachusetts Avenue, Cambridge, MA 02139, USADepartment of Astronomy, The Ohio State University , Columbus, OH 43210, USA; Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State University , Columbus, OH 43210, USA; Research School of Astronomy & Astrophysics, Australian National University , Cotter Road, Weston, ACT 2611, AustraliaOur understanding of the assembly timeline of the Milky Way has been transforming along with the dramatic increase in astrometric and spectroscopic data available over the past several years. Many substructures in chemo-dynamical space have been discovered and identified as the remnants of various galactic mergers. To investigate the timeline of these mergers, we select main-sequence turnoff and subgiant stars (MSTOs) from the H3 survey, finding members in seven metal-poor components of the halo: Gaia-Sausage/Enceladus (GSE), the Helmi Streams, Thamnos, Sequoia, Wukong/LMS-1, Arjuna, and I’itoi. We also select out a metal-poor in situ population to facilitate comparison to the evolution of the Milky Way itself at these early epochs. We fit individual isochrone ages to the MSTOs in each of these substructures and use the resulting age distributions to infer simple star formation histories (SFHs). For GSE, we resolve an extended SFH that truncates ≈10 Gyr ago, as well as a clear age–metallicity relation. From this age distribution and measured SFH we infer that GSE merged with the Milky Way at a time 9.5–10.2 Gyr ago, in agreement with previous estimates. We infer that the other mergers occurred at various times ranging from 9 to 13 Gyr ago, and that the metal-poor in situ Galaxy built up within only a few billion years. These results reinforce the emerging picture that both the disk and halo of the Milky Way experienced a rapid assembly.https://doi.org/10.3847/1538-4357/ad968eMilky Way stellar haloStellar agesMilky Way evolutionMilky Way formationGalaxy formationthe Milky Way |
| spellingShingle | Turner Woody Charlie Conroy Phillip Cargile Ana Bonaca Vedant Chandra Jiwon Jesse Han Benjamin D. Johnson Rohan P. Naidu Yuan-Sen Ting The Rapid Formation of the Metal-poor Milky Way The Astrophysical Journal Milky Way stellar halo Stellar ages Milky Way evolution Milky Way formation Galaxy formation the Milky Way |
| title | The Rapid Formation of the Metal-poor Milky Way |
| title_full | The Rapid Formation of the Metal-poor Milky Way |
| title_fullStr | The Rapid Formation of the Metal-poor Milky Way |
| title_full_unstemmed | The Rapid Formation of the Metal-poor Milky Way |
| title_short | The Rapid Formation of the Metal-poor Milky Way |
| title_sort | rapid formation of the metal poor milky way |
| topic | Milky Way stellar halo Stellar ages Milky Way evolution Milky Way formation Galaxy formation the Milky Way |
| url | https://doi.org/10.3847/1538-4357/ad968e |
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