Sub-gigayear variability around the star formation main sequence and its contribution to the scatter

¹ Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, Pl. Ciencias 1 Madrid 28040 Madrid, Spain
² Instituto de Física de Partículas y del Cosmos, Universidad Complutense de Madrid, Pl. Ciencias 1 Madrid 28040 Madrid, Spain
³ Instituto de Astronomía, Universidad Nacional Autónoma de México A.P. 106 Ensenada 22800 BC, Mexico
⁴ Instituto de Astrofísica de Canarias Vía Láctea s/n 38205 La Laguna Tenerife, Spain

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 13 May 2024
Accepted: 29 October 2025

Abstract

Aims. We aim to measure the evolution of individual galaxies around the star formation main sequence (SFMS) during the last gigayear as a function of their stellar mass to quantify how much of its scatter is due to short-term variability.

Methods. We derived star formation histories using full spectral fitting for a sample of 8960 galaxies from the MaNGA survey to track the position of the galaxies in the SFMS over the past gigayear.

Results. The variability correlates with both the stellar mass of the galaxies and their current position in both the SFMS and the mass-metallicity relation (MZR), with the position in the latter strongly affecting variability in the star formation rate. While most of the fluctuations are compatible with stochasticity, there is a very weak but statistically significant preference for ∼135 − 150 Myr timescales.

Conclusions. These results indicate that the star formation rate is strongly self-regulated within galaxies, establishing characteristic intensities and timescales for bursts of star formation and quenching episodes. We also find that short-term variability cannot account for the entirety of the scatter in the SFMS. It appears to originate to a similar degree in short-term variability and long-term (halo-level) differentiation and fits predictions from models.