The AIDA-TNG project: 3D halo shapes

¹ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna Via Piero Gobetti 93/3 I-40129 Bologna, Italy
² INFN – Sezione di Bologna Viale Berti Pichat 6/2 I-40127 Bologna, Italy
³ Dipartimento di Fisica e Astronomia “Augusto Righi”, Alma Mater Studiorum Università di Bologna Via Gobetti 93/2 I-40129 Bologna, Italy
⁴ Center for Particle Cosmology, University of Pennsylvania Philadelphia PA 19104, USA
⁵ Max-Planck-Institut für Astronomie Königstuhl 17 D-69117 Heidelberg, Germany
⁶ Department of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology Cambridge MA 02139, USA

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

Received: 4 December 2025
Accepted: 8 January 2026

Abstract

Context. The shapes of dark matter halos can be used to constrain the fundamental properties of dark matter. In standard cold dark matter (CDM) cosmologies, halos are typically triaxial, with a preference for prolate configurations; however, including the full baryonic physics tends to make them more oblate.

Aims. We focus on the characterization of total matter 3D shapes in alternative dark matter models, such as self-interacting dark matter (SIDM) and warm dark matter (WDM). These scenarios predict different structural properties due to collisional effects or the suppression of small-scale power.

Methods. We measured the different halo component shapes – dark matter, stars, and gas – at various radii from the center in AIDA-TNG (Alternative Interacting Dark Matter and Astrophysics – TNG), which is a suite of high-resolution cosmological simulations built upon the IllustrisTNG framework. The intent was to systematically study how different dark matter models – specifically SIDM and WDM – affect galaxy formation and the structure of dark matter halos when realistic baryonic physics is included.

Results. SIDM models tend to produce rounder and more isotropic halos, especially in the inner regions, as a result of momentum exchange between dark matter particles. Group- and cluster-size WDM halos are also slightly more spherical than their CDM counterparts. In all cases, the inclusion of self-consistent baryonic physics makes the central regions of all halos rounder, while still revealing clear distinctions among the various dark matter models, notably the self-interacting ones.

Conclusions. The general framework presented in this work, based on the 3D halo shape, can be useful for interpreting multiwavelength data analyses of galaxies and clusters.