Shaping the Milky Way: The interplay of mergers and cosmic filaments

Abstract

The large-scale morphology of Milky Way (MW)-mass dark matter (DM) 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 ($\ell =1$) and quadrupole ($\ell =2$) 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 ($\sim 30$ 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 multivariate Singular Spectrum Analysis, we successfully disentangle the effects of satellite mergers and filamentary accretion on quadrupole. We find that the quadrupolar response induced by LMC-mass satellites has an order of magnitude larger gravitational power than in spherically symmetric MW models. 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.

25 pages, 16 figures, Published in APJ

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Cited by in corpus (6)

• A Vertically Orientated Dark Matter Halo Marks a Flip of the Galactic Disk
• Dynamics of tidal spiral arms: Machine learning-assisted identification of equations and application to the Milky Way
• The dark matter wake of a galactic bar revealed by multichannel Singular Spectral Analysis
• Quantifying the Milky Way, LMC and their interaction using all-sky kinematics of outer halo stars
• Mapping the Distorted Dark Matter Distribution of the LMC-SMC System Prior to Milky Way Infall with Basis Function Expansions
• No Stream Left Unscathed: The imprint of a host galaxy