German astronomers conducted a study of the central convexity of the Andromeda galaxy and analyzed its stellar populations. This work can improve our understanding of the structure of convexity and the history of its formation.
The Andromeda spiral jumper galaxy (M31) is 2.5 million light-years distant from us and is the nearest large galaxy to the Milky Way. Due to proximity, it has become an excellent target for a detailed study of the evolutionary history of large spiral galaxies. The central bulge is important for such studies.
For the study, scientists used the 2.7-meter telescope at the MacDonald Observatory (Texas). This allowed us to obtain spectroscopic data M31. They were able to identify simple stellar characteristics of the population of the central region of the galaxy, including growth, metallicity and the presence of alpha elements.
M31 was monitored for 14 nights using a VIRUS-W integral field spectrograph. The survey covered the convexity area with a 1/3 fill factor and disk sampling in 6 different directions. The analysis showed that the age of central stellar populations is more than 10 billion years. For comparison, the stars of the galactic disk reach 5-6 billion years. Researchers also noticed that in the central 100 arcsecond, ancient metal-rich stars with a negative outward gradient and enhanced alpha elements dominate. The bulge and lintel (at the age of 10 and 13 billion years) are endowed with solar metals. The output indicates a two-step scenario of the formation of the internal area of the M31.
The classical stellar bulge is formed together with the original disk from a quasi-monolith collapse or a strong instability of a turbulent internal proto-disk. On a large scale, the proto-disk develops a jumper with old stars in the area. Further observations are planned for M31, which can shed light on the sequence of events creating the central sections of the galaxy.
