The origin of gas stripping of galaxies in group environments

¹ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095 98 bis bd Arago 75014 Paris, France
² Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
³ Department of Astronomy and Yonsei University Observatory, Yonsei University Seoul 03722, Republic of Korea
⁴ Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550 F-67000 Strasbourg, France
⁵ ILANCE, CNRS – University of Tokyo International Research Laboratory Kashiwa Chiba 277-8582, Japan
⁶ Kavli IPMU (WPI), UTIAS, The University of Tokyo Kashiwa Chiba 277-8583, Japan
⁷ Kyung Hee University, Dept. of Astronomy & Space Science Yongin-shi Gyeonggi-do 17104, Republic of Korea

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Received: 6 August 2025
Accepted: 10 November 2025

Abstract

We investigate how low-mass group environments (M_vir ∼ 10^{12 − 13} M_⊙) influence the gas content of their satellite galaxies with M_* > 10⁷ M_⊙ using the NEWHORIZON2 simulation. Many satellite galaxies preserve substantial gas reservoirs, yet show signs of outer gas stripping, reminiscent of jellyfish galaxies in clusters. In contrast, low-mass satellites (< 10⁸ M_⊙) are largely gas deficient, and some of them undergo gas removal within their host group by external pressure triggered by either galaxy interactions or ram pressure exerted by the hot intragroup medium. Complete gas removal in these satellite galaxies occurs when the external hydrodynamic pressure exceeds the gravitational restoring force, typically due to stochastic events such as galaxy-galaxy interactions or nearby galactic outflows. The emergence of a characteristic stellar mass of 10⁸ M_⊙, which determines the efficiency of gas removal in groups, likely reflects the differing scaling relations of external pressure with halo mass and gravitational restoring force with stellar mass. While tidal interactions can be a significant cause of gas loss in satellite galaxies, those severe enough to affect the gas content in the central regions typically lead to the complete disruption of the galaxy. Consequently, gas loss driven by tidal interactions may be underestimated in the studies focusing solely on surviving galaxies. Group environments, where environmental effects are weaker and satellite galaxies tend to have lower restoring forces due to their low masses, exhibit complex manifestations of gas loss that are not seen in more massive environments such as clusters.