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

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen, Germany
e-mail: camila.desafreitas@eso.org
² Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
⁴ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁵ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38200 La Laguna, Tenerife, Spain
⁷ Vyoma GmbH, Karl-Theodor-Str. 55, 80803 München, Germany
⁸ Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁹ Instituto de Física de Partículas y del Cosmos (IPARCOS), Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁰ Department of Astrophysics, University of Vienna, Türkenschanzstrasße 17, 1180 Wien, Austria
¹¹ Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Rua do Matão 1226, 05508-090 São Paulo, SP, Brazil
¹² European Space Agency, European Space Research and Technology Centre, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
¹³ Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea
¹⁴ Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, 146 Brownlow Hill, L3 5RF Liverpool, UK
¹⁵ Max Planck Institute for Astronomy, Königstuhl 17 69117, Germany
¹⁶ Institute of Cosmology and Gravitation, University of Portsmouth, Burnaby Road, Portsmouth PO1 3FX, UK
¹⁷ Observatorio Astronómico Nacional, C/Alfonso XII 3, Madrid 28014, Spain

Received: 2 August 2022
Accepted: 14 November 2022

Abstract

The epoch in which galactic discs settle is a major benchmark for testing models of galaxy formation and evolution but remains largely unknown. Once discs settle and become sufficiently self-gravitating, 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, 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 used integral field spectroscopic 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 formed. We demonstrate the methodology on the galaxy NGC 1433 – which we find to host an old bar that is 7.5_−1.1^+1.6(sys)_−0.5^+0.2(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 integral field spectroscopic 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.