Dr. Wang Chun from the Astrophysics Center of the School of Physics and Materials Science at Tianjin Normal University (TNU) has made significant progress in the field of the formation and evolution of the Milky Way, discovering that the chemical abundances of the Milky Way disk show obvious north - south asymmetry. The research results, titled "A North–South Metallicity Asymmetry in the Outer Galactic Disk—Evidence for the Pericentric Passage of the Sagittarius Dwarf Galaxy," were published online in "The Astrophysical Journal Letters."
Exploring the accretion and evolution history of the Milky Way is a core scientific issue for understanding galaxy formation and evolution, as well as an important current frontier direction. Based on red clump stars selected from the LAMOST and APOGEE survey data, the research team plotted the distribution of metallicity in the R-Z plane at different azimuth angles. The study found that in the inner disk of the Milky Way (R < 11 kpc), the galactic disk does not show obvious north - south asymmetry in metallicity. However, in the outer disk (R > 11 kpc), especially in the anti-galactic center direction (-5°<Φ< 15°), obvious north-south asymmetry in metallicity was found. In addition, this asymmetry is commonly present in each single-age stellar population. However, compared with the young stellar population (τ< 6 billion years), the significance of the asymmetry in the old stellar population (τ> 8 billion years) is lower. This reduction in significance may be due to three factors: larger uncertainties in age measurement, a smaller number of stars in the outer disk region, and the higher dynamic dispersion characteristics of the old stellar population itself. The study points out that this north-south asymmetry in metallicity may be jointly caused by the dynamic disturbance and tidal force generated by the pericentric passage of the Sagittarius Dwarf Galaxy through the galactic disk.
The figure shows the distribution of metallicity in the R-Z plane at different azimuth angles.
Dr. Wang Chun is the first and corresponding author, and TNU is the first affiliated institution. Associate Researcher Xie Lizhi from TNU, Associate Professor Huang Yang from the University of the Chinese Academy of Sciences, Professor Yuan Haibo from Beijing Normal University, Professor Timothy C. Beers from the University of Notre Dame in the United States, Dr. Payel Das from the University of Surrey in the United Kingdom, and Researcher Shao Shi from the National Astronomical Observatories also made important contributions to this study. The relevant work was funded by the Youth Project of the National Natural Science Foundation of China (12203037).
Paper link: https://iopscience.iop.org/article/10.3847/2041 - 8213/adf18a.
By He Jierui
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