Lunch talk on Apr. 28, 2025

Comparison of Two Formation Mechanisms of Barred Spiral Galaxies

Speaker: Yirui Zheng (SJTU)

Venue: SWIFAR Building 2111

Time: 12:45 PM, Monday, Apr. 28, 2025

Abstract: 

Galactic bars can form via the internal bar instability or external tidal perturbations by other galaxies. We systematically compare the properties of the bars formed through the two mechanisms with a series of controlled N-body simulations that form bars through internal or external mechanisms. We create three disk galaxy models with different dynamical “hotness” and evolve them in isolation and under flyby interactions. We then measure the bar properties, focusing on the pattern speed and exponential growth rate. In the cold- and warm-disk models, where bars can form spontaneously in isolation, tidally induced bars are promoted to a more “advanced” evolutionary stage. However, these bars have similar pattern speeds and growth timescales to those formed spontaneously within the same disk. In the hot-disk model, which avoids the internal bar instability in isolation, a bar forms only under perturbations and rotates/grows more slowly than those in the cold and warm disks. Thus, if “tidally induced bars” refer exclusively to those in galaxies that are otherwise stable against bar instability, they indeed rotate/grow more slowly than internally induced ones. However, these differences are due to the differences in the internal properties of the bar host galaxies, not the different formation mechanisms.

Report PPT:  SWIFAR_Yirui Zheng.pptx