Shaping the Milky Way: The Interplay of Mergers and Cosmic Filaments
Year: 2025
Type: article
Abstract: The large-scale morphology of Milky Way (MW)–mass dark matter halos is shaped by two key processes: filamentary accretion from the cosmic web and interactions with massive satellites. Disentangling their contributions is essential for understanding galaxy evolution and constructing accurate mass models of the MW. We analyze the time-dependent structure of MW-mass halos from zoomed cosmological-hydrodynamical simulations by decomposing their mass distribution into spherical harmonic expansions. We find that the dipole and quadrupole moments dominate the gravitational power spectrum, encoding key information about the halo’s shape and its interaction with the cosmic environment. While the dipole reflects transient perturbations from infalling satellites and damps on dynamical timescales, the quadrupole—linked to the halo’s triaxiality—is a persistent feature. We show that the quadrupole’s orientation aligns with the largest filaments, imprinting a long-lived memory on the halo’s morphology even in its inner regions (∼30 kpc). At the virial radius, the quadrupole distortion can reach 1–2 times the spherical density, highlighting the importance of environment in shaping MW-mass halos. Using multichannel singular spectrum analysis, we successfully disentangle the effects of satellite mergers and filamentary accretion on quadrupole. We find that, compared to isolated MW–LMC simulations that typically use a spherical halo, the LMC-mass satellite induces a quadrupolar response that is an order of magnitude larger in our cosmological halo. This highlights the need for models that incorporate the MW’s asymmetry and time evolution, with direct consequences for observable structures such as disk warps, the LMC-induced wake, and stellar tracers—particularly in the era of precision astrometry.
Source: The Astrophysical Journal
Institutions: University of Washington, University of Pennsylvania, University of Arizona, Flatiron Institute, University of Massachusetts Amherst, Royal Observatory, University of Edinburgh, University of La Serena, Columbia University, Centre National de la Recherche Scientifique, Kavli Institute for the Physics and Mathematics of the Universe, Université Paris Cité, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, CY Cergy Paris Université, Institut de Ciències del Cosmos, Universitat de Barcelona, The University of Tokyo, University of Surrey, Stanford University, California Institute of Technology, Carnegie Observatories
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W4412636405