# Clocking the assembly of double-barred galaxies with the MUSE TIMER project

## TL;DR

This study investigates the formation and longevity of double-barred galaxies using MUSE observations, revealing that inner bars are likely formed from small-scale discs and are long-lived structures over several billion years.

## Contribution

It provides observational evidence supporting the dynamical formation of inner bars from small-scale discs and constrains their assembly epochs, advancing understanding of galaxy evolution.

## Key findings

- Inner bars are associated with inner discs of similar size.
- Inner bars in studied galaxies formed over 4.5-6.5 billion years ago.
- Inner bars are long-lived, stable structures.

## Abstract

The formation of two stellar bars within a galaxy has proved challenging for numerical studies. It is yet not clear whether the inner bar is born via a star formation process promoted by gas inflow along the outer bar, or whether it is dynamically assembled from instabilities in a small-scale stellar disc. Observational constraints to these scenarios are scarce. We present a thorough study of the stellar content of two double-barred galaxies observed by the MUSE TIMER project, NGC 1291 and NGC 5850, combined with a two-dimensional multi-component photometric decomposition performed on the 3.6{\mu}m images from S4G. Our analysis confirms the presence of {\sigma}-hollows appearing in the stellar velocity dispersion distribution at the ends of the inner bars. Both galaxies host inner discs matching in size with the inner bars, suggestive of a dynamical formation for the inner bars from small-scale discs. The analysis of the star formation histories for the structural components shaping the galaxies provides constraints on the epoch of dynamical assembly of the inner bars, which took place >6.5 Gyr ago for NGC 1291 and >4.5 Gyr ago for NGC 5850. This implies that inner bars are long-lived structures.