The role of environment in the evolution of disc galaxy density profiles

New insights from simulations and comparison to Euclid data

Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France

^⋆ Corresponding author: maelie.mondelin@cea.fr

Received: 28 March 2025
Accepted: 12 June 2025

Abstract

Galactic discs are known to have exponential radial profiles in luminosity and in stellar surface density, in their bright inner regions. Nonetheless, their faint outer regions often display a break in the profile, with either a down-bending break or an up-bending break of the density profile. Recent Euclid Early Release Observations have shown that down-bending breaks are very scarce in the Perseus cluster, which was already suspected with poorer statistics in the Virgo cluster. We use hydrodynamic simulations of disc galaxies interacting with a Perseus-like cluster. We show that Type II profiles – corresponding to down-bending disc breaks – can be rapidly eroded by the cluster tidal field on a timescale of approximately 1 Gyr, while Type III profiles – associated with up-bending breaks – and Type I profiles – with no significant break – remain largely unaffected. Type II profiles are eroded through a combination of dynamical processes, including tidal stirring of pre-existing stars by the cluster potential, and triggering of new star formation in the outer disc. Overall, our simulations show that observations of disc breaks across different environments and cosmic epochs are consistent with a coherent evolutionary picture. At high redshift, observations by JWST of disc galaxies reveal early break structures formed in relatively isolated environments. At low redshift, isolated disc galaxies in field environments continue to exhibit these break features, while dense cluster environments, as observed by Euclid in the Perseus cluster, show significant alterations to these profiles. Our findings support a scenario in which down-bending disc break profiles result primarily from internal dynamical processes – such as disc instabilities and resonances – during early formation phases, and are later modified by environmental effects in dense clusters. This interpretation does not require invoking additional mechanisms such as ram-pressure stripping or variations in star formation density thresholds to explain the observed evolution of down-bending breaks among disc galaxies at various redshifts and in various environments.