The structure of the Milky Way disk at different scales

Abstract:

Understanding the formation and evolution of the galaxies has been a topic of interest for centuries. Studying the Milky Way provides a unique advantage, allowing us to investigate individual stars in great detail due to our favourable position within the galaxy. However, our vantage point within the Disk presents challenges in mapping its complete structure. Nevertheless, astronomers have made remarkable progress in unravelling the different structural components of our Galaxy. While it is well known that our galaxy is a barred spiral galaxy, the finer details, such as the number and position of arms, remain subjects of ongoing debate.

In order to map our galactic disk in more detail, we focused on studying the distribution of red clump stars, an indicator of the intermediate-to-old age population. We extracted the largest catalogue of 8.8 million red clump stars from 2MASS colour-magnitude diagrams in the Galactic disk. The resulting distribution of red clump stars in the Galactic plane revealed the presence of the Outer arm of the Galaxy with an extension of 6 kpc in comparison to the earlier known limits. Additionally, we explore the use of interstellar dust, primarily confined to the Galactic disk, to trace the structure. We carried out polarisation observation of distant open clusters in different directions to demonstrate the role of polarisation as a tool to provide insights into small and large-scale dust features in the Galactic Disk. Our study successfully indicates the presence of large spiral arms and some low-density structures in the inter-arm region. In addition to the structural information, the results provide strong evidences of the large-scale magnetic field alignment along the spiral arms of the Galaxy. A brief summary of these results will be presented in the seminar.