Modelling the selection of galaxy groups with end-to-end simulations

Seppi R, Eckert D, Finoguenov A, Shreeram S, Tempel E, Gozaliasl G, Lorenz M, Wilms J, Mamon GA, Gastaldello F, Lovisari L, O’Sullivan E, Kolokythas K, Bourne MA, Sun M, Pillepich A (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Astronomy & Astrophysics EDP Sciences

Book Volume: 699

Article Number: A206

DOI: 10.1051/0004-6361/202553977

Abstract

Context. Feedback from supernovae and active galactic nuclei (AGN) shapes the galaxy formation and evolution, but its impact remains unclear. Galaxy groups offer a crucial probe to determine this impact because their gravitational binding energy is comparable to the energy that is available from their central AGN. The XMM-Newton Group AGN Project (X-GAP) is a sample of 49 groups that were selected in the X-ray (ROSAT) and optical (SDSS) bands and provides a benchmark for hydrodynamical simulations. Aims. For this comparison, it is essential to understand the selection effects. We model the selection function of X-GAP by forward-modelling the detection process in the X-ray and optical bands. Methods. Using the Uchuu N-body simulation, we built a dark matter halo light cone, predicted X-ray group properties with a neural network trained on hydrodynamical simulations, and assigned matching observed properties to the galaxies. We compared the selected sample to the parent population in the light cone. Results. Our method provided a sample that matched the observed distribution of the X-ray luminosity and velocity dispersion. A completeness of 50% was reached at a velocity dispersion of 450 km/s in the X-GAP redshift range. The selection is driven by X-ray flux, with a secondary dependence on the velocity dispersion and redshift. We estimated a purity level of 93% for the X-GAP parent sample. We calibrated the relation of the velocity dispersion to the halo mass. We found a normalisation and slope that agree with the literature and an intrinsic scatter of about 0.06 dex. The measured velocity dispersion is only accurate within 10% for rich systems with more than about 20 members, and the velocity dispersion for groups with fewer than 10 members is biased at more than 20%. Conclusions. The X-ray follow-up refines the optical selection and enhances the purity, but reduces completeness. In an SDSS-like setup, measurement errors for the velocity dispersion dominate the intrinsic scatter. Our selection model enables unbiased comparisons of thermodynamic properties and gas fractions between X-GAP groups and hydrodynamical simulations.

Authors with CRIS profile

Maximilian Lorenz Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut Jörn Wilms Lehrstuhl für Astronomie und Astrophysik

Involved external institutions

Institut d'astrophysique de Paris FR France (FR) National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) IT Italy (IT) Smithsonian Institution US United States (USA) (US) Rhodes University ZA South Africa (ZA) University of Hertfordshire GB United Kingdom (GB) University of Alabama in Huntsville (UAH) US United States (USA) (US) Max-Planck-Institut für Astronomie / Max Planck Institute for Astronomy (MPIA) DE Germany (DE) University of Geneva / Université de Genève (UNIGE) CH Switzerland (CH) Helsingin yliopisto / University of Helsinki FI Finland (FI) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics DE Germany (DE) University of Tartu EE Estonia (EE)

How to cite

APA:

Seppi, R., Eckert, D., Finoguenov, A., Shreeram, S., Tempel, E., Gozaliasl, G.,... Pillepich, A. (2025). Modelling the selection of galaxy groups with end-to-end simulations. Astronomy & Astrophysics, 699. https://doi.org/10.1051/0004-6361/202553977

MLA:

Seppi, R., et al. "Modelling the selection of galaxy groups with end-to-end simulations." Astronomy & Astrophysics 699 (2025).

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