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Date and Time of the Query: 2019-05-24 T10:07:07 PDT
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For refcode 2014MNRAS.443.1688D:
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Copyright by Royal Astronomical Society. 2014MNRAS.443.1688D Balancing mass and momentum in the Local Group Diaz, J. D.; Koposov, S. E.; Irwin, M.; Belokurov, V.; Evans, N. W. Abstract. In the rest frame of the Local Group (LG), the total momentum of the Milky Way (MW) and Andromeda (M31) should balance to zero. We use this fact to constrain new solutions for the solar motion with respect to the LG centre of mass, the total mass of the LG, and the individual masses of M31 and the MW. Using the set of remote LG galaxies at >350 kpc from the MW and M31, we find that the solar motion has amplitude V_sun_ = 299 +/- 15 km s^-1^ in a direction pointing towards galactic longitude l_sun_ = 98.4^degree^ +/- 3.6^degree^ and galactic latitude b_sun_ = -5.9^degree^ +/- 3.0^degree^. The velocities of M31 and the MW in this rest frame give a direct measurement of their mass ratio, for which we find log_10_(M_M31_/M_MW_) = 0.36 +/- 0.29. We combine these measurements with the virial theorem to estimate the total mass within the LG as M_LG_ = (2.5 +/- 0.4) x 10^12^ M_sun_. Our value for M_LG_ is consistent with the sum of literature values for M_MW_ and M_M31_. This suggests that the mass of the LG is almost entirely located within the two largest galaxies rather than being dispersed on larger scales or in a background medium. The outskirts of the LG are seemingly rather empty. Combining our measurement for M_LG_ and the mass ratio, we estimate the individual masses of the MW and M31 to be M_MW_ = (0.8 +/- 0.5) x 10^12^ M_sun_ and M_M31_ = (1.7 +/- 0.3) x 10^12^ M_sun_, respectively. Our analysis favours M31 being more massive than the MW by a factor of ~2.3, and the uncertainties allow only a small probability (9.8 per cent) that the MW is more massive. This is consistent with other properties such as the maximum rotational velocities, total stellar content, and numbers of globular clusters and dwarf satellites, which all suggest that M_M31_/M_MW_ > 1. Key words: Galaxy: halo, galaxies: dwarf, galaxies: individual: M31, galaxies: kinematics and dynamics, Local Group
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