과제 10. Dual nature of the Galactic halo

• 개괄

  • The halo of the Milky Way (MW) has long been thought to have one stellar component. However, in recent years, various observational evidence has emerged indicating that the MW halo can be largely divided into two distinct stellar components, the so-called inner- and outer-halo populations, based on their differing spatial distribution, kinematics, and metallicity. One might expect that this distinction should also appear in other chemical abundances, such as carbon (e.g., [C/Fe]) and alpha ([α/Fe]) among metal-poor halo stars. In order to test this hypothesis, we would like to consider MP and especially CEMP stars. The chemical characteristics for the halo population(s) will provide powerful new evidence for the existence of the multiple stellar components of the Milky Way’s halo, and their likely origin.

     

• 질문

  • What is the general trend of the metallicity and carbon abundance for the inner- and outer-halo populations?

  • Is there a difference in the fraction of the CEMP subclasses (CEMP-s and CEMP-no) between the inner and outer halo stars?

  • Is there any similarity in the carbon abundance and the fraction of two of the CEMP subclasses between the halo stars (especially the outer-halo stars) and the ultra-faint dwarf (UFD) galaxies around the Milky Way? If so, what can that reveal about the formation of the Milky Way?

     

• 참고 논문

  1. “Carbon-enhanced Metal-poor Stars: CEMP-s and CEMP-no Subclasses in the Halo System of the Milky Way” by Carollo et al., 2014, ApJ, 788, 180

  2. “Carbon-enhanced Metal-poor Stars in the Inner and Outer Halo Components of the Milky Way” by Carollo et al., 2012, ApJ, 744, 195

  3. “Near-Field Cosmology with Extremely Metal-Poor Stars” by Frebel & Norris, 2015, ARA&A, 53, 631