Resolving local and global kinematic signatures of satellite mergers with billion particle simulations

Abstract

In this work we present two new ∼ 10 9 particle self-consistent simulations of the merger of a Sagittarius-like dwarf galaxy with a Milky Way-like disc galaxy. One model is a violent merger creating a thick disc, and a Gaia-Enceladus/Sausage like remnant. The other is a highly stable disc which we use to illustrate how the improved phase space resolution allows us to better examine the formation and evolution of structures that have been observed in small, local volumes in the Milky Way, such as the z − v z phase spiral and clustering in the v R − v φ plane when compared to previous works. The local z − v z phase spirals are clearly linked to the global asymmetry across the disc: we find both 2-armed and 1-armed phase spirals, which are related to breathing and bending behaviors respectively. Hercules-like moving groups are common, clustered in v R − v φ in local data samples in the simulation. These groups migrate outwards from the inner galaxy, matching observed metallicity trends even in the absence of a galactic bar. We currently release the best fitting 'present day' merger snapshots along with the unperturbed galaxies for comparison.

Exploring the Sgr-Milky-Way-disc interaction using high resolution N-body simulations

“…The amplitude is clearly not what we see in the Gaia data, but it is difficult to tell how the period of the spiral compares to the data given the weak signal. Other works with well resolved spirals typically have Sgr mass models on the order of our Heavy Sgr (Laporte et al 2019;Hunt et al 2021), therefore the faint spiral in our Medium and Light Sgr model is not unexpected. After looking at how changing mass affects the perturbation to the solar neighbourhood, it is safe to conclude that the median velocity orbit for any of the models will not result in a match to the Gaia DR2 data.…”

“…Which means we cannot force it to exactly match the mid-plane density of the Milky Way disc, something BB21 shows can affect the perturbation wavelength and amplitude. The lack of a gas disc is also a limitation of our simulations, though it is a fairly common simplification (Laporte et al 2018;Hunt et al 2021) and simply assumes that the gas approximately follows the stars. Finally, from our analysis in Section 3.3, we see that the mass of the halo, and therefore dynamical friction, has a large effect on the observed perturbation.…”

“…By utilising a GPU 𝑁-body tree-code, we are able to overcome this and quickly run simulations with 500 million to 1 billion particles (e.g. Hunt et al 2021). Vasiliev & Belokurov (2020) perform an in depth analysis of the kinematics of Sgr including finding the mass of the progenitor, ∼ (4 ± 1) × 10 8 M , where approximately 25% comes from the stellar component.…”

Bending Waves in Velocity Space: a First Look at the THINGS sample

“…Using a toy model, Binney & Schönrich (2018) show that the phase spiral can be the result of a coevolution of both density wave and bending wave generated by the crossing of Sagittarius Dwarf through the Galactic disc about 0.5 Gyr ago. These discoveries fuelled a frenzy of parallelly evolving simulations (Gómez et al, 2013(Gómez et al, , 2016(Gómez et al, , 2017(Gómez et al, , 2021Bland-Hawthorn et al, 2019;Bland-Hawthorn & Tepper-García, 2021;Laporte et al, 2019;Chequers & Widrow, 2017;Chequers et al, 2018;Grion Filho et al, 2021;Hunt et al, 2021;Schönrich & Dehnen, 2018;Widrow et al, 2014;Khoperskov et al, 2019) that were able to reproduce these substructures as due to bending waves generated under different scenarios.…”

“…A number of physical mechanisms have been put forward to generate the bending waves in disc galaxies, such as tidal interaction with satellites or companion galaxies (Hunter & Toomre, 1969; Edelsohn & Elmegreen, 1997; Weinberg, 1998;Weinberg & Blitz, 2006;Gómez et al, 2013;Widrow et al, 2014;Gómez et al, 2016Gómez et al, , 2017Schönrich & Dehnen, 2018;Bland-Hawthorn et al, 2019;Laporte et al, 2019;Bland-Hawthorn & Tepper-García, 2021;Gómez et al, 2021;Grion Filho et al, 2021;Hunt et al, 2021); intergalactic matter accreted onto the dark halo (Jiang & Binney, 1999) or directly onto the disc (López-Corredoira et al, 2002); intergalactic magnetic field (Battaner et al, 1990) and intergalactic wind (Kahn & Woltjer, 1959). Bending waves are shown to also arise, from various internal instabilities (Araki, 1985;Revaz & Pfenniger, 2004;Sellwood, 1996;Chequers & Widrow, 2017), from resonant coupling (Binney, 1981), due to the dynamical friction between a disc and its halo (Nelson & Tremaine, 1995) and even due to the halo substructure (Chequers et al, 2018).…”