A new method for age-dating the formation of bars in disc galaxies: The TIMER view on NGC1433's old bar and the inside-out growth of its nuclear disc

TL;DR

This paper introduces a new method to determine the age of galactic bars by analyzing the star formation history of nuclear discs using integral field spectroscopic data, providing insights into galaxy formation and evolution.

Contribution

The paper presents a novel methodology for estimating bar ages through nuclear disc star formation histories, validated on NGC 1433, linking bar formation to nuclear disc development.

Findings

NGC 1433 hosts an old bar approximately 8 Gyr old.

Nuclear disc growth in NGC 1433 follows an inside-out formation pattern.

Methodology can be applied to other barred galaxies with high-resolution IFS data.

Abstract

The epoch in which galactic discs settle is a major benchmark to test models of galaxy formation and evolution but is as yet largely unknown. Once discs settle and become self-gravitating enough, stellar bars are able to form; therefore, determining the ages of bars can shed light on the epoch of disc settling, and on the onset of secular evolution. Nevertheless, until now, timing when the bar formed has proven challenging. In this work, we present a new methodology for obtaining the bar age, using the star formation history of nuclear discs. Nuclear discs are rotation-supported structures, built by gas pushed to the centre via bar-induced torques, and their formation is thus coincident with bar formation. In particular, we use integral field spectroscopic (IFS) data from the TIMER survey to disentangle the star formation history of the nuclear disc from that of the underlying main disc, which enables us to more accurately determine when the nuclear disc forms. We demonstrate the methodology on the galaxy NGC 1433 -- which we find to host an old bar that is $8.0^{+1.6}_{-1.1}\rm{(sys)}^{+0.2}_{-0.5}\rm{(stat)}$ Gyr old -- and describe a number of tests carried out on both the observational data and numerical simulations. In addition, we present evidence that the nuclear disc of NGC 1433 grows in accordance with an inside-out formation scenario. This methodology is applicable to high-resolution IFS data of barred galaxies with nuclear discs, making it ideally suited for the TIMER survey sample. In the future we will thus be able to determine the bar age for a large sample of galaxies, shedding light on the epoch of disc settling and bar formation.