Diverse lifestyles of bar-like galaxies and their coevolution with the brightest galaxy in the most massive cluster of TNG50

Abstract

Clusters can provide propitious environments for bar formation in galaxies. This work studies the formation and evolution of 15 bar-like galaxies in the most massive cluster of the TNG50 simulation from the IllustrisTNG suite. The selection includes galaxies from the last simulation output from well-resolved subhalos with a strongly prolate stellar component. Eleven galaxies form or strongly enhance their bars during a pericenter passage around one or more progenitors of the brightest cluster galaxy (BCG). Two form their bars early as a result of minor mergers, one via an interaction with another massive galaxy, and one via disk instability. The bar formation times differ considerably, ranging between 3-11 Gyr. The lengths of the bars also differ, ranging between 2-6 kpc, and do not correlate with the amount of tidal forcing experienced. All galaxies have at least one pericenter passage around a BCG progenitor, but the number of interactions varies strongly and is reflected in the different amount of mass stripping the galaxies experience. Most bar formation events take place before the BCG is fully formed. In three cases, they occur just before different progenitors of the BCG merge. For six bar-like galaxies, the merger events leading to the final formation of the BCG cause significant changes of their orbits. Their diverse evolutionary histories illustrate the different paths to bar formation in clusters and emphasize the complex nature of the process, which includes coevolution with BCG progenitors.

Figures (7)

• Figure 1: Surface density maps of the stellar component of 15 bar-like galaxies in face-on view at $z = 0$. Galaxies are identified by their subhalo ID numbers at $z = 0$, shown on the right of each panel. The color scale is adjusted to the maximum and minimum density of each galaxy and the contours are equally spaced in log surface density.
• Figure 2: Evolution of different measures of shape over time for 15 bar-like galaxies. Lines show the axis ratios $b/a$ (blue), $c/a$ (red), the triaxiality parameter $T$ (green), the rotation parameter $f$ (magenta), and the bar mode $A_2$ (black). Galaxies are identified by their subhalo ID numbers at $z = 0$, shown on the right of each panel. Vertical dashed lines indicate the time of bar formation.
• Figure 3: Evolution of the total mass over time for 15 bar-like galaxies. Lines show the total galaxy mass in dark matter (blue), stars (red), and gas (green). The dark masses are given in units of $10^{11}$ M$_\odot$, while the stellar and gas masses are in units of $10^{10}$ M$_\odot$. Galaxies are identified by their subhalo ID numbers at $z = 0$, shown on the right of each panel. Vertical dashed lines indicate the time of bar formation.
• Figure 4: Distances from perturbers as a function of time for 15 bar-like galaxies. Different colored lines show the distances from distinct perturbers, with data for ID0 shown in blue in all panels. Galaxies are identified by their subhalo ID numbers at $z = 0$, shown on the right of each panel. Vertical dashed lines indicate the time of bar formation.
• Figure 5: Evolution of the profile of the bar mode, $A_2 (R)$, over time for five galaxies from the first columns of Figs. \ref{['surden']}-\ref{['neighbors']}. The galaxies are identified by their subhalo ID numbers at $z = 0$ given on the right of each panel. The reddest color corresponds to regions with no stars bound to the galaxy.