Galaxy formation with wave/fuzzy dark matter: The core-halo structure and the solitonic imprint

¹ University of the Basque Country UPV/EHU, Department of Theoretical Physics, Bilbao E-48080, Spain
² DIPC, Basque Country UPV/EHU, E-48080 San Sebastian, Spain
³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁵ Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550, USA
⁶ Ikerbasque, Basque Foundation for Science, Bilbao E-48011, Spain
⁷ Hong Kong University of Science and Technology, Institute for Advanced Study and Department of Physics, IAS TT & WF Chao Foundation Professor, Hong Kong
⁸ Energetic Cosmos Laboratory, Nazarbayev University, Nursultan, Kazakhstan
⁹ Paris Centre for Cosmological Physics, APC, AstroParticule et Cosmologie, Université de Paris, CNRS/IN2P3, CEA/lrfu, Université Sorbonne Paris Cité, 10, Rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13, France
¹⁰ Physics Department & LBNL, University of California at Berkeley, CA 94720, Emeritus, Berkeley, USA
¹¹ Department of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹² Black Hole Initiative at Harvard University, 20 Garden Street, Cambridge, MA 02138, USA

^⋆ Corresponding authors: alvaro.pozolarrocha@bizkaia.eu, tom.j.broadhurst@gmail.com

Received: 19 April 2024
Accepted: 31 May 2025

Abstract

Dark matter-dominated cores have long been claimed for the well-studied local group dwarf galaxies. More recently, extended stellar halos have been uncovered around several of these dwarfs through deeper imaging and spectroscopy. Such core-halo structures (inner flat core and a characteristic r⁻³ asymptotic outer halo profile) are not a feature of conventional cold dark matter (CDM). In contrast, smooth and prominent dark matter cores are predicted for wave/fuzzy dark matter (ψDM). The question arises as to what extent the visible stellar profiles should reflect this dark matter core structure. Here we compare cosmological hydrodynamical simulations of CDM, “WDM” (model used as a proxy for ψDM) & ψDM, aiming to predict the stellar profiles for these three DM scenarios. We show that cores surrounded by extended halos are distinguishable for ψDM, where the stellar density is enhanced in the core due to the presence of the relatively dense soliton. Our analysis demonstrates that, in our simulations, a distinctive core-halo structure does not appear in the case of CDM in the DM, gas, or stars. Whereas we do find a core-halo transition for DM, gas, and stars for ψDM, and the scale of this transition is in line with the predicted core radius set by the soliton scale anticipated for the adopted boson mass of 2.5×10⁻²² eV. The presence of a core-halo structure in the stellar profile for Galaxy 1 for ψDM is visible for the most massive and the first galaxy to form in the simulation. Clearly, further simulations are needed to establish how strict this possible relationship is between the DM and stellar core-halo profile as a potential observational discriminator. Furthermore, we observe the anticipated asymmetry for ψDM due to the soliton's motion (jumping and random walk), a distinctive characteristic not found in the symmetric distributions of stars in the warm and CDM models.