Stellar spiral structures in triaxial dark matter haloes

Abstract

We employ very high resolution simulations of isolated Milky Way-like galaxies to study the effect of triaxial dark matter haloes on exponential stellar discs. Nonadiabatic halo shape changes can trigger two-armed grand-design spiral structures which extend all the way to the edge of the disc. Their pattern speed coincides with the inner Lindblad resonance indicating that they are kinematic density waves which can persist up to several Gyr. In dynamically cold discs, grand-design spirals are swing amplified and after a few Gyr can lead to the formation of (multi-armed) transient recurrent spirals. Stellar discs misaligned to the principal planes of the host triaxial halo develop characteristic integral shaped warps, but otherwise exhibit very similar spiral structures as aligned discs. For the grand-design spirals in our simulations, their strength dependence with radius is determined by the torque on the disc, suggesting that by studying grand-design spirals without bars it may be possible to set constraints on the tidal field and host dark matter halo shape.

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

“…where M * = 9.5 × 10 9 M is the total mass of the disc, RS = 3.13 kpc is the scale length of the disc and z0 = 0.1 RS is the scale height of the disc. We choose these parameters so that they match with the high-Q disc in Hu & Sijacki (2016). As shown in Hu & Sijacki (2016), high-Q disc responds to external torques, but does not form any noticeable self-gravity-induced spiral structures due to its low surface density, thus enabling us to focus on the kinematic properties.…”

“…As shown in Hu & Sijacki (2016), high-Q disc responds to external torques, but does not form any noticeable self-gravity-induced spiral structures due to its low surface density, thus enabling us to focus on the kinematic properties. Also, as found in Hu & Sijacki (2016), stellar discs, setup to be in equilibrium within a spherical halo, develop two-armed grand-design spirals when placed in a triaxial halo directly. To avoid this and study the effect of subhaloes, we grow the disc in an adiabatically changing dark matter halo, explained in detail in Section 2.3.…”

“…In fact, stellar discs are in general found to be very sensitive to perturbations, including massive molecular clouds (D'Onghia et al 2013) and large-scale torques (Dubinski & Chakrabarty 2009;DeBuhr et al 2012). In particular, Hu & Sijacki (2016) found that a realistic triaxial dark matter halo can lead to two-armed grand-design spiral structures. Given that subhaloes exist widely in dark matter haloes, it is necessary to understand their interactions with the spiral structures.…”

“…Gravity-induced spiral structures may develop in strong self-gravitating discs (see e.g. Sellwood & Carlberg 2014;Hu & Sijacki 2016). Flocculent, re-current, multi-armed spiral structures form in this scenario.…”

“…Due to the high-Q profile of the stellar disc, the swing amplification is weak. We therefore do not need higher number of particles to prevent transient gravity-induced spiral structures from forming (for further details see Hu & Sijacki 2016). The stellar disc is initially in equilibrium with a spherical halo, and as shown in Hu & Sijacki (2016) it will develop strong twoarmed spirals if we put it directly into our smooth triaxial dark matter halo model.…”