Unveiling a Young Thick Disk in the Milky Way
The thickness of a galaxy’s disk provides a valuable probe of its formation and evolution history. Observations of the Milky Way and local galaxies have revealed an ubiquitous disk structure with two distinctive components: an old thick disk and a relatively young thin disk. The formation of this du...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/adccb7 |
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| author | Jianhui Lian Min Du Shuai Lu Bingqiu Chen Gail Zasowski Zhaoyu Li Xiaojie Liao Chao Liu |
| author_facet | Jianhui Lian Min Du Shuai Lu Bingqiu Chen Gail Zasowski Zhaoyu Li Xiaojie Liao Chao Liu |
| author_sort | Jianhui Lian |
| collection | DOAJ |
| description | The thickness of a galaxy’s disk provides a valuable probe of its formation and evolution history. Observations of the Milky Way and local galaxies have revealed an ubiquitous disk structure with two distinctive components: an old thick disk and a relatively young thin disk. The formation of this dual-disk structure and the mechanisms that develop the thickness of the disk are still unclear. Whether the disk thickness is inherited from the birth environment or is established through secular dynamical heating after formation is under debate. In this work, we identify a relatively young (∼6.6 billion yr old), geometric thick disk in the Milky Way, with a scale height of 0.64 kpc at the solar circle. This young, thick component exhibits comparable thickness and flaring strength to the canonical old thick disk but is more radially extended and systematically younger. We also identify thin disk components that formed before and after this young thick disk. Detailed analysis of the solar vicinity structure suggests that the young thick disk marks the onset of a new phase of upside-down disk formation. These findings strongly discount the role of secular dynamical heating and support a turbulent, bursty birth environment as the primary mechanism behind thick disk formation. The existence of two thick disk components suggests that the Milky Way has undergone at least two episodes of turbulent and bursty star formation, likely triggered by galaxy mergers. |
| format | Article |
| id | doaj-art-2b666b7b09f94b8f97d6940d6c6a370c |
| institution | DOAJ |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal Letters |
| spelling | doaj-art-2b666b7b09f94b8f97d6940d6c6a370c2025-08-20T02:43:31ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019842L4810.3847/2041-8213/adccb7Unveiling a Young Thick Disk in the Milky WayJianhui Lian0https://orcid.org/0000-0001-5258-1466Min Du1https://orcid.org/0000-0001-9953-0359Shuai Lu2https://orcid.org/0009-0006-5658-414XBingqiu Chen3https://orcid.org/0000-0003-2472-4903Gail Zasowski4https://orcid.org/0000-0001-6761-9359Zhaoyu Li5https://orcid.org/0000-0001-5017-7021Xiaojie Liao6https://orcid.org/0009-0003-8415-556XChao Liu7https://orcid.org/0000-0002-1802-6917South-Western Institute for Astronomy Research, Yunnan University , Kunming, Yunnan 650091, People’s Republic of China ; jianhui.lian@ynu.edu.cnDepartment of Astronomy, Xiamen University, Xiamen, Fujian 361005, People’s Republic of China ; dumin@xmu.edu.cnDepartment of Astronomy, Xiamen University, Xiamen, Fujian 361005, People’s Republic of China ; dumin@xmu.edu.cnSouth-Western Institute for Astronomy Research, Yunnan University , Kunming, Yunnan 650091, People’s Republic of China ; jianhui.lian@ynu.edu.cnDepartment of Physics & Astronomy, University of Utah , Salt Lake City, UT 84112, USADepartment of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University , 800 Dongchuan Road, Shanghai 200240, People’s Republic of ChinaDepartment of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University , 800 Dongchuan Road, Shanghai 200240, People’s Republic of ChinaNational Astronomical Observatories, Chinese Academy of Sciences , Beijing 100012, People’s Republic of China; University of Chinese Academy of Sciences , Beijing 100049, People’s Republic of ChinaThe thickness of a galaxy’s disk provides a valuable probe of its formation and evolution history. Observations of the Milky Way and local galaxies have revealed an ubiquitous disk structure with two distinctive components: an old thick disk and a relatively young thin disk. The formation of this dual-disk structure and the mechanisms that develop the thickness of the disk are still unclear. Whether the disk thickness is inherited from the birth environment or is established through secular dynamical heating after formation is under debate. In this work, we identify a relatively young (∼6.6 billion yr old), geometric thick disk in the Milky Way, with a scale height of 0.64 kpc at the solar circle. This young, thick component exhibits comparable thickness and flaring strength to the canonical old thick disk but is more radially extended and systematically younger. We also identify thin disk components that formed before and after this young thick disk. Detailed analysis of the solar vicinity structure suggests that the young thick disk marks the onset of a new phase of upside-down disk formation. These findings strongly discount the role of secular dynamical heating and support a turbulent, bursty birth environment as the primary mechanism behind thick disk formation. The existence of two thick disk components suggests that the Milky Way has undergone at least two episodes of turbulent and bursty star formation, likely triggered by galaxy mergers.https://doi.org/10.3847/2041-8213/adccb7Milky Way GalaxyGalaxy structureGalaxy stellar disksStellar populationsChemical abundancesGalaxy evolution |
| spellingShingle | Jianhui Lian Min Du Shuai Lu Bingqiu Chen Gail Zasowski Zhaoyu Li Xiaojie Liao Chao Liu Unveiling a Young Thick Disk in the Milky Way The Astrophysical Journal Letters Milky Way Galaxy Galaxy structure Galaxy stellar disks Stellar populations Chemical abundances Galaxy evolution |
| title | Unveiling a Young Thick Disk in the Milky Way |
| title_full | Unveiling a Young Thick Disk in the Milky Way |
| title_fullStr | Unveiling a Young Thick Disk in the Milky Way |
| title_full_unstemmed | Unveiling a Young Thick Disk in the Milky Way |
| title_short | Unveiling a Young Thick Disk in the Milky Way |
| title_sort | unveiling a young thick disk in the milky way |
| topic | Milky Way Galaxy Galaxy structure Galaxy stellar disks Stellar populations Chemical abundances Galaxy evolution |
| url | https://doi.org/10.3847/2041-8213/adccb7 |
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