Birth of the Galactic Disk Revealed by the H3 Survey
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arXiv
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| Autores principales: | , , , , , , , , , , , , , , |
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| Formato: | Preprint |
| Publicado: |
2022
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| author | Conroy, Charlie Weinberg, David H. Naidu, Rohan P. Buck, Tobias Johnson, James W. Cargile, Phillip Bonaca, Ana Caldwell, Nelson Chandra, Vedant Han, Jiwon Jesse Johnson, Benjamin D. Speagle, Joshua S. Ting, Yuan-Sen Woody, Turner Zaritsky, Dennis |
| author_facet | Conroy, Charlie Weinberg, David H. Naidu, Rohan P. Buck, Tobias Johnson, James W. Cargile, Phillip Bonaca, Ana Caldwell, Nelson Chandra, Vedant Han, Jiwon Jesse Johnson, Benjamin D. Speagle, Joshua S. Ting, Yuan-Sen Woody, Turner Zaritsky, Dennis |
| contents | We use chemistry ([alpha/Fe] and [Fe/H]), main sequence turnoff ages, and kinematics determined from H3 Survey spectroscopy and Gaia astrometry to identify the birth of the Galactic disk. We separate in-situ and accreted stars on the basis of angular momenta and eccentricities. The sequence of high-alpha in-situ stars persists down to at least [Fe/H]=-2.5 and shows unexpected non-monotonic behavior: with increasing metallicity the population first declines in [alpha/Fe], then increases over the range -1.3<[Fe/H]<-0.7, and then declines again at higher metallicities. The number of stars in the in-situ population rapidly increases above [Fe/H]=-1. The average kinematics of these stars are hot and independent of metallicity at [Fe/H]<-1 and then become increasingly cold and disk-like at higher metallicities. The ages of the in-situ, high-alpha stars are uniformly very old (13 Gyr) at [Fe/H]<-1.3, and span a wider range (8-12 Gyr) at higher metallicities. Interpreting the chemistry with a simple chemical evolution model suggests that the non-monotonic behavior is due to a significant increase in star formation efficiency, which began 13 Gyr ago. These results support a picture in which the first 1 Gyr of the Galaxy was characterized by a "simmering phase" in which the star formation efficiency was low and the kinematics had substantial disorder with some net rotation. The disk then underwent a dramatic transformation to a "boiling phase", in which the star formation efficiency increased substantially, the kinematics became disk-like, and the number of stars formed increased tenfold. We interpret this transformation as the birth of the Galactic disk at z~4. The physical origin of this transformation is unclear and does not seem to be reproduced in current galaxy formation models. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2204_02989 |
| institution | arXiv |
| publishDate | 2022 |
| record_format | arxiv |
| spellingShingle | Birth of the Galactic Disk Revealed by the H3 Survey Conroy, Charlie Weinberg, David H. Naidu, Rohan P. Buck, Tobias Johnson, James W. Cargile, Phillip Bonaca, Ana Caldwell, Nelson Chandra, Vedant Han, Jiwon Jesse Johnson, Benjamin D. Speagle, Joshua S. Ting, Yuan-Sen Woody, Turner Zaritsky, Dennis Astrophysics of Galaxies We use chemistry ([alpha/Fe] and [Fe/H]), main sequence turnoff ages, and kinematics determined from H3 Survey spectroscopy and Gaia astrometry to identify the birth of the Galactic disk. We separate in-situ and accreted stars on the basis of angular momenta and eccentricities. The sequence of high-alpha in-situ stars persists down to at least [Fe/H]=-2.5 and shows unexpected non-monotonic behavior: with increasing metallicity the population first declines in [alpha/Fe], then increases over the range -1.3<[Fe/H]<-0.7, and then declines again at higher metallicities. The number of stars in the in-situ population rapidly increases above [Fe/H]=-1. The average kinematics of these stars are hot and independent of metallicity at [Fe/H]<-1 and then become increasingly cold and disk-like at higher metallicities. The ages of the in-situ, high-alpha stars are uniformly very old (13 Gyr) at [Fe/H]<-1.3, and span a wider range (8-12 Gyr) at higher metallicities. Interpreting the chemistry with a simple chemical evolution model suggests that the non-monotonic behavior is due to a significant increase in star formation efficiency, which began 13 Gyr ago. These results support a picture in which the first 1 Gyr of the Galaxy was characterized by a "simmering phase" in which the star formation efficiency was low and the kinematics had substantial disorder with some net rotation. The disk then underwent a dramatic transformation to a "boiling phase", in which the star formation efficiency increased substantially, the kinematics became disk-like, and the number of stars formed increased tenfold. We interpret this transformation as the birth of the Galactic disk at z~4. The physical origin of this transformation is unclear and does not seem to be reproduced in current galaxy formation models. |
| title | Birth of the Galactic Disk Revealed by the H3 Survey |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2204.02989 |