Kinematic and metallicity of the dwarf spheroidal galaxy Andromeda XVIII
Kateryna Kvasova, Evan N. Kirby, Rachael L. Beaton
arXiv:2404.11804v1 Announce Type: new
Abstract: Andromeda XVIII is an isolated dwarf galaxy 579 kpc away from the nearest large galaxy, M31. It is a candidate “backsplash galaxy” that might have been affected by a close passage to M31. We present new Keck/DEIMOS spectroscopy of Andromeda XVIII to assess the likelihood that it is a backsplash galaxy. We estimated the velocities, metallicities ([Fe/H]), and $alpha$-enhancements ([$alpha$/Fe]) for 56 probable members. We estimated Andromeda XVIII’s mean heliocentric velocity, rotation velocity, position angle of the rotation axis, and velocity dispersion using maximum likelihood coupled with a Monte Carlo Markov chain (MCMC). There is no evidence for bulk rotation, though sub-populations might be rotating. The mean heliocentric velocity is -337.2 km s$^{-1}$. The line-of-sight velocity relative to M31 is -36 km s$^{-1}$ (approaching), which is lower than the escape velocity from M31. Based on the abundances of 38 stars with low errors ($delta [Fe/H] arXiv:2404.11804v1 Announce Type: new
Abstract: Andromeda XVIII is an isolated dwarf galaxy 579 kpc away from the nearest large galaxy, M31. It is a candidate “backsplash galaxy” that might have been affected by a close passage to M31. We present new Keck/DEIMOS spectroscopy of Andromeda XVIII to assess the likelihood that it is a backsplash galaxy. We estimated the velocities, metallicities ([Fe/H]), and $alpha$-enhancements ([$alpha$/Fe]) for 56 probable members. We estimated Andromeda XVIII’s mean heliocentric velocity, rotation velocity, position angle of the rotation axis, and velocity dispersion using maximum likelihood coupled with a Monte Carlo Markov chain (MCMC). There is no evidence for bulk rotation, though sub-populations might be rotating. The mean heliocentric velocity is -337.2 km s$^{-1}$. The line-of-sight velocity relative to M31 is -36 km s$^{-1}$ (approaching), which is lower than the escape velocity from M31. Based on the abundances of 38 stars with low errors ($delta [Fe/H]