BANG-MaNGA: A census of kinematic discs and bulges across mass and star formation in the local Universe

¹ DiSAT, Università degli Studi dell’Insubria, Via Valleggio 11, 22100 Como, Italy
² INAF – Osservatorio Astronomico di Brera, Via Brera 20, 20121 Milano, Italy
e-mail: fabio.rigamonti@inaf.it
³ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
⁴ Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
⁵ International Centre for Radio Astronomy Research, The University of Western Australia, Crawley, WA 6009, Australia
⁶ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁷ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany

Received: 9 January 2024
Accepted: 14 March 2024

Abstract

In this work, we aim to quantify the relevance of kinematically identified bulges and discs and their role in the process of galaxy quenching. To achieve this, we utilised an analysis of the SDSS-MaNGA survey conducted with the GPU-based code BANG which simultaneously models galaxy photometry and kinematics to decompose galaxies into their structural components. We found that below M_⋆ ≃ 10¹¹ M_⊙, galaxies span a wide range in their dynamical properties. The overall dynamical state of a galaxy is determined by the relative prominence of a dispersion-supported inner region and a rotationally supported disc. Our decomposition reveals a natural separation between these classes, with only a minor fraction of stellar mass retained by structures exhibiting intermediate dynamical support. When examining galaxies in terms of their star formation activity, an apparent substantial decrease in rotational support is observed as they move below the star-forming main sequence. This behaviour is particularly evident when using luminosity-weighted tracers of kinematics, while it almost vanishes with mass-weighted tracers. Luminosity-weighted quantities not only capture differences in kinematics but also in the stellar population, potentially leading to biased interpretations of galaxy dynamical properties and quenching. Our findings indicate that quenching implies almost no any structural transformation in galaxies below M_⋆ ≃ 10¹¹ M_⊙. Processes such as disc fading are more likely explanations for the observed differences in mass-weighted and luminosity-weighted galaxy properties. When the galactic disc ceases star formation, its mass-to-light ratio does indeed increase without any significant morphological transformation. The picture is remarkably different above M_⋆ ≃ 10¹¹ M_⊙. In this case, regardless of the tracer used, a substantial increase in galaxy dispersion support is observed along with a significant structural change. A different quenching mechanism, most likely associated with mergers, dominates. Notably, this mechanism is confined to a very limited range of high masses.