The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data
We present an analysis of the structure, kinematics, and chemo-dynamical properties of the Milky Way bulge using RR Lyrae stars from Optical Gravitational Lensing Experiment (OGLE), and giant stars from APOGEE and Gaia that have distances placing them in the inner Galaxy. First, using a sample of 18...
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2025-01-01
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| author | Xiao Han Hai-Feng Wang Giovanni Carraro Martín López-Corredoira Yuan-Sen Ting Yang-Ping Luo Guan-Yu Wang (MWLUDPSG Collaboration) |
| author_facet | Xiao Han Hai-Feng Wang Giovanni Carraro Martín López-Corredoira Yuan-Sen Ting Yang-Ping Luo Guan-Yu Wang (MWLUDPSG Collaboration) |
| author_sort | Xiao Han |
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| description | We present an analysis of the structure, kinematics, and chemo-dynamical properties of the Milky Way bulge using RR Lyrae stars from Optical Gravitational Lensing Experiment (OGLE), and giant stars from APOGEE and Gaia that have distances placing them in the inner Galaxy. First, using a sample of 1879 ab-type RR Lyrae stars (RRabs) from OGLE-IV, we identified three populations: central bulge RRabs, the inner bulge RRabs, and halo or disk interlopers, based on their apocenters derived from orbital integration. Inner bulge RRabs kinematically align with the Galactic bar, while central bulge RRabs show slower rotation with lower velocity dispersion. Higher velocity dispersion stars were identified as halo/disk interlopers. Then, an orbital analysis of 28,188 APOGEE Red Clump and Red Giant Branch stars revealed kinematic properties consistent with RRabs, and the chemical abundance distribution displayed a bimodal stellar density pattern, suggesting complex star evolution histories and slightly different star formation histories for the inner bulge and central bulge. The differences in the density distribution on the ∣ Z ∣ _max -eccentricity plane for the central bulge, inner bulge, and interlopers are clearly detected. It is found that the classification of bulge stars based on orbital parameters, rather than solely on metallicity, provides a more accurate population separation. As the inner bulge, which contains the highest fraction of stars, traces the bar formed by the instability of the Galactic disk, our results support that the pseudobulge is the primary origin of the bulge. Furthermore, fitting the observed data to both the boxy and X-shaped bulge models indicated a preference for the boxy bulge. |
| format | Article |
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| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-a1d50af985874ee3a5697c45223e640c2025-08-20T02:15:24ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198513210.3847/1538-4357/adc4e5The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia DataXiao Han0Hai-Feng Wang1https://orcid.org/0000-0001-8459-1036Giovanni Carraro2https://orcid.org/0000-0002-0155-9434Martín López-Corredoira3https://orcid.org/0000-0001-6128-6274Yuan-Sen Ting4https://orcid.org/0000-0001-5082-9536Yang-Ping Luo5Guan-Yu Wang6(MWLUDPSG Collaboration)Department of Astronomy, China West Normal University , Nanchong 637002, People’s Republic of China ; hfwang@bao.ac.cnDepartment of Astronomy, China West Normal University , Nanchong 637002, People’s Republic of China ; hfwang@bao.ac.cn; Dipartimento di Fisica e Astronomia “Galileo Galilei,” Universitá degli Studi di Padova , Vicolo Osservatorio 3, I-35122, Padova, Italy ; haifeng.wang.astro@gmail.comDipartimento di Fisica e Astronomia “Galileo Galilei,” Universitá degli Studi di Padova , Vicolo Osservatorio 3, I-35122, Padova, Italy ; haifeng.wang.astro@gmail.comInstituto de Astrofísica de Canarias , E-38205 La Laguna, Tenerife, Spain; Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife, SpainDepartment of Astronomy, The Ohio State University , Columbus, OH 43210, USA; Center for Cosmology and AstroParticle Physics, The Ohio State University , Columbus, OH 43210, USADepartment of Astronomy, China West Normal University , Nanchong 637002, People’s Republic of China ; hfwang@bao.ac.cnDepartment of Astronomy, China West Normal University , Nanchong 637002, People’s Republic of China ; hfwang@bao.ac.cnWe present an analysis of the structure, kinematics, and chemo-dynamical properties of the Milky Way bulge using RR Lyrae stars from Optical Gravitational Lensing Experiment (OGLE), and giant stars from APOGEE and Gaia that have distances placing them in the inner Galaxy. First, using a sample of 1879 ab-type RR Lyrae stars (RRabs) from OGLE-IV, we identified three populations: central bulge RRabs, the inner bulge RRabs, and halo or disk interlopers, based on their apocenters derived from orbital integration. Inner bulge RRabs kinematically align with the Galactic bar, while central bulge RRabs show slower rotation with lower velocity dispersion. Higher velocity dispersion stars were identified as halo/disk interlopers. Then, an orbital analysis of 28,188 APOGEE Red Clump and Red Giant Branch stars revealed kinematic properties consistent with RRabs, and the chemical abundance distribution displayed a bimodal stellar density pattern, suggesting complex star evolution histories and slightly different star formation histories for the inner bulge and central bulge. The differences in the density distribution on the ∣ Z ∣ _max -eccentricity plane for the central bulge, inner bulge, and interlopers are clearly detected. It is found that the classification of bulge stars based on orbital parameters, rather than solely on metallicity, provides a more accurate population separation. As the inner bulge, which contains the highest fraction of stars, traces the bar formed by the instability of the Galactic disk, our results support that the pseudobulge is the primary origin of the bulge. Furthermore, fitting the observed data to both the boxy and X-shaped bulge models indicated a preference for the boxy bulge.https://doi.org/10.3847/1538-4357/adc4e5Galactic bulgeMilky Way diskMilky Way Galaxy physics |
| spellingShingle | Xiao Han Hai-Feng Wang Giovanni Carraro Martín López-Corredoira Yuan-Sen Ting Yang-Ping Luo Guan-Yu Wang (MWLUDPSG Collaboration) The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data The Astrophysical Journal Galactic bulge Milky Way disk Milky Way Galaxy physics |
| title | The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data |
| title_full | The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data |
| title_fullStr | The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data |
| title_full_unstemmed | The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data |
| title_short | The Structure, Populations, and Kinematics of the Milky Way Central and Inner Bulge with OGLE, APOGEE, and Gaia Data |
| title_sort | structure populations and kinematics of the milky way central and inner bulge with ogle apogee and gaia data |
| topic | Galactic bulge Milky Way disk Milky Way Galaxy physics |
| url | https://doi.org/10.3847/1538-4357/adc4e5 |
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