Galaxies in the central regions of simulated galaxy clusters

¹ Dipartimento di Fisica e Astronomia “Augusto Righi”, Alma Mater Studiorum Universitá di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
e-mail: antonio.ragagnin@unibo.it
² INAF – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34143 Trieste, Italy
³ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
⁴ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy
⁵ INFN-Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
⁶ Centre for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
⁷ Instituto de Astronomía Teórica y Experimental (IATE), Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET), Universidad Nacional de Córdoba, Laprida 854, X5000BGR Córdoba, Argentina
⁸ Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
⁹ Dipartimento di Fisica, Université degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
¹⁰ Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr.1, 81679 München, Germany
¹¹ Astronomy Unit, Department of Physics, University of Trieste, Via Tiepolo 11, 34131 Trieste, Italy
¹² Max-Planck-Institut für Astrophysik (MPA), Karl-Schwarzschild Strasse 1, 85748 Garching bei München, Germany
¹³ INAF – IASF Milano, Via A. Corti 12, 20133 Milano, Italy
¹⁴ INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹⁵ Department of Astronomy, Yale University, New Haven, CT, USA
¹⁶ Dipartimento di Fisica e Scienze della Terra, Universitá degli Studi di Ferrara, Via Saragat 1, 44122 Ferrara, Italy, Zürich, Switzerland

Received: 27 March 2022
Accepted: 14 June 2022

Abstract

Context. Recent observations found that observed cluster member galaxies are more compact than their counterparts in ΛCDM hydrodynamic simulations, as indicated by the difference in their strong gravitational lensing properties, and they reported that measured and simulated galaxy–galaxy strong lensing events on small scales are discrepant by one order of magnitude. Among the possible explanations for this discrepancy, some studies suggest that simulations with better resolution and implementing different schemes for galaxy formation could produce simulations that are in better agreement with the observations.

Aims. In this work, we aim to assess the impact of numerical resolution and of the implementation of energy input from AGN feedback models on the inner structure of cluster sub-haloes in hydrodynamic simulations.

Methods. We compared several zoom-in re-simulations of a sub-sample of cluster-sized haloes obtained by varying mass resolution and softening the length and AGN energy feedback scheme. We studied the impact of these different setups on the sub-halo (SH) abundances, their radial distribution, their density and mass profiles, and the relation between the maximum circular velocity, which is a proxy for SH compactness

Results. Regardless of the adopted numerical resolution and feedback model, SHs with masses of M_SH ≲ 10¹¹ h⁻¹ M_⊙, the most relevant mass range for galaxy–galaxy strong lensing, have maximum circular velocities ∼30% smaller than those measured from strong lensing observations. We also find that simulations with less effective AGN energy feedback produce massive SHs (M_SH ≳ 10¹¹ h⁻¹ M_⊙) with higher maximum circular velocity and that their V_max − M_SH relation approaches the observed one. However, the stellar-mass number count of these objects exceeds the one found in observations, and we find that the compactness of these simulated SHs is the result of an extremely over-efficient star formation in their cores, also leading to larger than observed SH stellar mass.

Conclusions. Regardless of the resolution and galaxy formation model adopted, simulations are unable to simultaneously reproduce the observed stellar masses and compactness (or maximum circular velocities) of cluster galaxies. Thus, the discrepancy between theory and observations that emerged previous works. It remains an open question as to whether such a discrepancy reflects limitations of the current implementation of galaxy formation models or the ΛCDM paradigm.