Impact of merger histories on the timing argument estimate of the Local Group mass

Abstract

The timing argument (TA) aims to find the total mass of the Local Group (LG) from the relative motions of the Milky Way (MW) and Andromeda Galaxy (M31). However, the classical TA always overestimates the LG mass, presumably because it does not account for the hierarchical scenario and other interactions such as that with the Large Magellanic Cloud (LMC). We focus on the impact of the recent major merger at M31 by using three merger models to find the peculiar motion of M31 within the simple two-body and point-mass scenario of TA. We found that the merger correction may affect the TA mass by either plus or minus 10-15% depending on the M31 tangential motion, which has very large uncertainties. If we consider a M31 merger configuration that reduces the TA mass by 10-15% to which we add the impact due to the LMC infall into the MW as reported in the literature, the TA mass would be found consistent with the LG mass from Hubble-Lemaitre flow. Galaxies are expected to experience about 16 major mergers each since z=11.5. Assuming all these mergers have similar impact on the TA mass as the most recent M31 merger, the ratio of LG mass to TA mass would be $0.85_{-0.37}^{+0.65}$ and such a TA mass is consistent with all the LG mass estimates. Our result also agrees with the findings using LG analogues in the cosmological simulations. We find that the TA mass estimate is limited by the hierarchical scenario, since it not possible to track the progenitors of both MW and M31 through so many mergers. We conclude that the MW-M31 dynamical system is far too complex to be modelled as a simple two-body point mass system.

Accepted in Astronomy and Astrophysics, February 14th 2025, 5 pages, 4 Figures

References in corpus (20)

• Gaia Early Data Release 3: The astrometric solution
• The M31 Velocity Vector. II. Radial Orbit Towards the Milky Way and Implied Local Group Mass
• Improved GRAVITY astrometric accuracy from modeling of optical aberrations
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• A dynamical model of the local cosmic expansion
• Detection of the Milky Way reflex motion due to the Large Magellanic Cloud infall
• Detection of the Keplerian decline in the Milky Way rotation curve
• Balancing mass and momentum in the Local Group
• Ram pressure stripping of an isolated Local Group dwarf galaxy: evidence for an intra-group medium
• Toward a Complete Understanding of the Magellanic Stream Formation
• A sub-2% Distance to M31 from Photometrically Homogeneous Near-Infrared Cepheid Period-Luminosity Relations Measured with the Hubble Space Telescope
• Milky Way total Mass derived by Rotation Curve and Globular Cluster kinematics from Gaia EDR3
• The Local Group Mass in the light of Gaia
• Implications of the Milky Way travel velocity for dynamical mass estimates of the Local Group
• Local Group timing argument and virial theorem mass estimators from cosmological simulations
• The survey of planetary nebulae in Andromeda (M31) VI. Kinematics of M31 inner-halo substructures and comparison with major-merger simulation predictions
• Weighing Milky Way and Andromeda in an expanding $\Lambda$CDM Universe: Decreasing the Local Group mass
• Reassessing the proper motions of M31/M33 with Gaia DR3. Unraveling systematic uncertainties
• The Milky Way accretion history compared to cosmological simulations -- from bulge to dwarf galaxy infall
• Dark matter fraction derived from the M31 rotation curve