A holistic review of a galactic interaction

Douglas Grion Filho,Ronald Drimmel,Eloisa Poggio,Elena D’Onghia,Chervin F P Laporte,Kathryn V Johnston

doi:10.1093/mnras/stab2398

Abstract

ABSTRACT Our situation as occupants of the Milky Way (MW) Galaxy, bombarded by the Sagittarius dwarf galaxy, provides an intimate view of physical processes that can lead to the dynamical heating of a galactic disc. While this evolution is instigated by Sagittarius, it is also driven by the intertwined influences of the dark matter halo and the disc itself. We analyse an N-body simulation following a Sagittarius-like galaxy interacting with a MW-like host to disentangle these different influences during the stages of a minor merger. The accelerations in the disc plane from each component are calculated for each snapshot in the simulation, and then decomposed into Fourier series on annuli. The analysis maps quantify and compare the scales of the individual contributions over space and through time: (i) accelerations due to the satellite are only important around disc passages; (ii) the influence around these passages is enhanced and extended by the distortion of the dark matter halo; (iii) the interaction drives disc asymmetries within and perpendicular to the plane and the self-gravity of these distortions increase in importance with time eventually leading to the formation of a bar. These results have interesting implications for identifying different influences within our own Galaxy. Currently, Sagittarius is close enough to a plane crossing to search for localized signatures of its effect at intermediate radii, the distortion of the MW’s dark matter halo should leave its imprint in the outer disc and the disc’s own self-consistent response is sculpting the intermediate and inner disc.

Highlights

There has been a significant revision in our perception of the Milky Way, shifting from an equilibrium picture to one rife with signatures of disequilibrium, as revealed by large-scale stellar surveys
The m = 0 terms amplitude and sign reflects the outward propagating rings in density during the early part of the simulation. It is dominated by the net change in mass distribution, which results in a decrease/increase in the attractive force in the inner/outer disc
We mapped accelerations caused by the three main protagonists (Sgr, Galactic disc, and DM halo) on to the Galactic disc in the radial, azimuthal, and vertical directions

Summary

Introduction

There has been a significant revision in our perception of the Milky Way (hereafter MW), shifting from an equilibrium picture to one rife with signatures of disequilibrium, as revealed by large-scale stellar surveys.North/South asymmetries in density and velocity structure were found in the Galactic disc using data from SDSS Widrow et al (2012) and Williams et al (2013). Analysis of LAMOST and RAVE suggested these local asymmetries to be part of a large-scale vertical wave (Carlin et al 2013; Xu et al 2015). In the plane of the disc, several kinematic ridges in the U − V velocity plane have been revealed in the Solar neighborhood (Gaia Collaboration 2018b; Ramos, Antoja & Figueras 2018). Other ridges have been shown in the (R, vT) plane (Antoja et al 2018; Kawata et al 2018; Laporte et al 2020) and in action space (Trick, Coronado & Rix 2019). Gaia Collaboration (2018b), Friske & Schonrich (2019), and Eilers et al (2020) have shown both local and global spiral waves in mean galactocentric radial velocities. Several dynamical processes could explain their origin, such as spiral arms (Quillen 2003; Quillen & Minchev 2005; Hunt et al 2019; Sellwood et al 2019; Khoperskov et al 2020), bar resonances (Fragkoudi et al 2019, 2020; Hunt et al 2019; Monari et al 2019; Kawata et al 2020; Laporte et al 2020; Trick et al 2021), or the response of the disc to an infalling satellite (Minchev et al 2009; Gomez et al 2012; Antoja et al 2018; Khanna et al 2019; Laporte et al 2019)

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