Impact of cosmological satellites on stellar discs: dissecting one satelliteat a time

Abstract

Within the standard hierarchical structure formation scenario, Milky Way-mass dark matter haloes have hundreds of dark matter subhaloes with mass 10 8 M . Over the lifetime of a galactic disc a fraction of these may pass close to the central region and interact with the disc. We extract the properties of subhaloes, such as their mass and trajectories, from a realistic cosmological simulation to study their potential effect on stellar discs. We find that massive subhalo impacts can generate disc heating, rings, bars, warps, lopsidedness as wells as spiral structures in the disc. Specifically, strong counter-rotating single-armed spiral structures form each time a massive subhalo passes through the disc. Such single-armed spirals wind up relatively quickly (over 1 − 2 Gyrs) and are generally followed by co-rotating two-armed spiral structures that both develop and wind up more slowly. In our simulations self-gravity in the disc is not very strong and these spiral structures are found to be kinematic density waves. We demonstrate that there is a clear link between each spiral mode in the disc and a given subhalo that caused it, and by changing the mass of the subhalo we can modulate the strength of the spirals. Furthermore, we find that the majority of subhaloes interact with the disc impulsively, such that the strength of spirals generated by subhaloes is proportional to the total torque they exert. We conclude that only a handful of encounters with massive subhaloes is sufficient for re-generating and sustaining spiral structures in discs over their entire lifetime.

Accretion of small satellites and gas inflows in a disc galaxy

“…Although the latter used orbits derived from cosmological simulations. Similarly, the simulations by Hu & Sijacki (2018), which use satellites with properties extracted from cosmological simulations in the same mass range as our satellites, show similar morphological features. However, neither Kazantzidis et al (2009) nor Hu & Sijacki (2018) included hydrodynamics.…”

“…Other orbits may be less effective in moving such gas quantities to the inner regions. Recent works have focused on reproducing features in spiral galaxies expected to be produced by minor interactions (e. g. Dobbs et al 2010;Chakrabarti & Blitz 2009;Chakrabarti et al 2011;Pettitt et al 2016;Hu & Sijacki 2018;Shah et al 2019).…”

Testing gravity with wide binary stars like α Centauri

“…Bars and spiral features in galaxies can be triggered by interactions with satellites (Hu & Sijacki 2018). However, without disk self-gravity, any spirals formed in this way would rapidly wind up and decay due to differential rotation of the disk (Fall & Lynden-Bell 1981, page 111).…”

Inside Out and Upside-Down: The Roles of Gas Cooling and Dynamical Heating in Shaping the Stellar Age-Velocity Relation

“…An alternative explanation for the origin of the AVR is that older stars were born dynamically hotter in the past, but that the disk "settles" and becomes progressively cooler as the star forming gas cools with time. The stars might be dynamically hotter in the past due to a more active galaxy merger phase (Toth & Ostriker 1992;Quinn et al 1993;Brook et al 2004;Martig et al 2014;Hu & Sijacki 2018;Buck et al 2020) or due to the fact that gravitational turbulence is higher if the disk is more gas rich , or due to a higher star formation rate (SFR; e.g., Lehnert et al 2014).…”