Bars and spirals in tidal interactions with an ensemble of galaxy mass models

Abstract

We present simulations of the gaseous and stellar material in several different galaxy mass models under the influence of different tidal fly-bys to assess the changes in their bar and spiral morphology. Five different mass models are chosen to represent the variety of rotation curves seen in nature. We find a multitude of different spiral and bar structures can be created, with their properties dependent on the strength of the interaction. We calculate pattern speeds, spiral wind-up rates, bar lengths, and angular momentum exchange to quantify the changes in disc morphology in each scenario. The wind-up rates of the tidal spirals follow the 2:1 resonance very closely for the flat and dark matter dominated rotation curves, whereas the more baryon dominated curves tend to wind-up faster, influenced by their inner bars. Clear spurs are seen in most of the tidal spirals, most noticeable in the flat rotation curve models. Bars formed both in isolation and interactions agree well with those seen in real galaxies, with a mixture of "fast" and "slow" rotators. We find no strong correlation between bar length or pattern speed and the interaction strength. Bar formation is, however, accelerated/induced in four out of five of our models. We close by briefly comparing the morphology of our models to real galaxies, easily finding analogues for nearly all simulations presenter here, showing passages of small companions can easily reproduce an ensemble of observed morphologies.

The evolution of pitch angles of spiral arms

“…Our finding that the distribution of pitch angles (cot α) is more or less uniform among their observed galaxies, opens up the possibility that the pitch angles are actually evolving in time, as is found in the simulations (e.g. Grand et al 2013;Pettitt & Wadsley 2018;Mata-Chávez et al 2019). We note that in the modal density wave picture, this finding would need some other explanation.…”

Effects of Gas on Formation and Evolution of Stellar Bars and Nuclear Rings in Disk Galaxies

“…It appears that the bar pattern speed as well as R are affected by various parameters such galaxy rotation curve, gas fraction, halo shape, etc. (e.g., Athanassoula 2014;Pettitt & Wadsley 2018). For instance, Pettitt & Wadsley (2018) showed that the bar pattern speed depends rather critically on the shape of the rotation curve in such a way that bars under the "rising" rotation curve are slow, while the other rotation curves produce fast bars.…”

Galaxy Zoo: unwinding the winding problem – observations of spiral bulge prominence and arm pitch angles suggest local spiral galaxies are winding

“…As a concrete example, Pettitt & Wadsley (2018) investigate the dependence of pattern speeds and wind-up rates on morphology in a sample of 5 model galaxies (designed to mimic M31, NGC4414, M33, M81 and the Milky Way). They were interested in investigating the impact of changing bar and disk properties, however, bulge mass also varies between their models, and there is a clear suggestion in their results that the wind-up rate is affected by bulge mass.…”