Speaker
Description
Recent observations around the M31 have revealed many traces of past interactions with satellite galaxies. In particular, the Andromeda Giant Southern Stream (AGSS) in the halo and the double ring structure in the disc have been drawing attention. The AGSS is a giant structure extending more than 100 kpc from the center of M31 and is thought to have been formed in a collision with a satellite galaxy about 80 billion years ago (Fardal et al. 2007; Mori & Rich 2008). On the other hand, Block et al. (2006) found the double ring structure in M31 made up of gas and dust and argued that the structure was formed by a head-on collision of a satellite galaxy, M32, around 20 billion years ago. They conclude that the mass of M32 at the time of the collision was about one-tenth of the total mass of M31 $\sim 10^{11} M_\odot$. Moreover, a model has been proposed by Hammer et al. (2018) in which the AGSS and the double ring structure are formed simultaneously by a major merger with the mass of more than $10^{11} M_\odot$ for the first passage at the large pericentric distance.
These situations motivate us to investigate the possible link between the AGSS and the 10kpc ring structures using $N$-body/SPH simulations of a miner merger between the M31 and a satellite galaxy with a mass of $10^{10} M_\odot$. The simulation result successfully matches the observed features of the AGSS and the 10 kpc rings concurrently. The stars are smoothly distributed in the galactic disk, but there are some rings of gas and dust that reproduce the observations. In addition, we demonstrate the spatial metallicity distribution of the merger remnants, assuming the progenitor galaxy's metallicity gradient. The result remarkably captures the observed features in the AGSS exhibiting non-uniform metallicity distribution perpendicular to the AGSS axis (Preston et al. 2021). These results indicate that a minor merger of the massive dwarf galaxy is also capable of simultaneously forming the AGSS and the 10 kpc ring.
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