The Milky Way accretion history compared to cosmological simulations -- from bulge to dwarf galaxy infall

Abstract

Galactic halos are known to grow hierarchically, inside out. This implies a correlation between the infall lookback time of satellites and their binding energy. Cosmological simulations predict a linear relation between the infall lookback time and the logarithm of the binding energy, with a small scatter. Gaia measurements of the bulk proper motions of globular clusters and dwarf satellites of the Milky Way are sufficiently accurate to establish the kinetic energies of these systems. Assuming the gravitational potential of the Milky Way, we can deduce the binding energies of the dwarf satellites and those of the galaxies that were previously accreted by the Milky Way. This can be compared to cosmological simulations for the first time. The relation of the infall lookback time versus binding energy we found in a cosmological simulation matches that for the early accretion events when the simulated total Milky Way mass within 21 kpc was rescaled to 2 $10^{11}$ solar masses. This agrees well with previous estimates from globular cluster kinematics and from the rotation curve. However, the vast majority of the dwarf galaxies are clear outliers to this rescaled relation, unless they are very recent infallers. In other words, the very low binding energies of most dwarf galaxies compared to Sgr and previous accreted galaxies suggests that most of them were accreted much later than 8 or even 5 Gyr ago. We also found that the subhalo systems in some cosmological simulations are too dynamically hot when they are compared to identified Milky Way substructures. This leads to an overestimated impact of satellites on the Galaxy rotation curve.

A&A Letters Volume 692, December 2024, 5 pages, 2 Figures, and Appendix A & B, the late infall of dwarf galaxies is supported by the discovery of young stars in dSphs by Yang et al. 2024, see arXiv:2409.15414

References in corpus (16)

• galpy: A Python Library for Galactic Dynamics
• The Global Dynamical Atlas of the Milky Way mergers: Constraints from Gaia EDR3 based orbits of globular clusters, stellar streams and satellite galaxies
• Reconstructing the Last Major Merger of the Milky Way with the H3 Survey
• Analytical properties of Einasto dark matter haloes
• Public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation
• Detection of the Keplerian decline in the Milky Way rotation curve
• Mapping the Milky Way Disk with Gaia DR3: 3D extended kinematic maps and rotation curve to $\approx 30$ kpc
• The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy
• Uncertainties associated with the backward integration of dwarf satellites using simple parametric potentials
• Mass models of the Milky Way and estimation of its mass from the GAIA DR3 data-set
• Determination of Dark Matter Halo Mass from Dynamics of Satellite Galaxies
• Most pseudo-bulges can be formed at later stages of major mergers
• The accretion history of the Milky Way. I. How it shapes globular clusters and dwarf galaxies
• On the Galactic rotation curve inferred from the Jeans equations Assessing its robustness using Gaia DR3 and cosmological simulations
• Galaxy archaeology for wet mergers: Globular cluster age distributions in the Milky Way and nearby galaxies
• Determining Satellite Infall Times Using Machine Learning

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