Merge and strip: Dark matter-free dwarf galaxies in clusters can be formed by galaxy mergers

Abstract

Context. Recent observations of galaxy mergers inside galaxy cluster environments, such as NGC 5291 in the vicinity of Abell 3574, report high star formation rates in the ejected tidal tails, which point towards currently developing tidal dwarf galaxies. This prompts the intriguing question whether these newly formed stellar structures could get stripped from the galaxy potential by the cluster and thus populate it with dwarf galaxies. Aims. We verify whether environmental stripping of tidal dwarf galaxies from galaxy mergers inside galaxy cluster environments is a possible evolutionary channel to populate a galaxy cluster with low-mass and low surface brightness galaxies. Methods. We performed three high-resolution hydrodynamical simulations of mergers between spiral galaxies in a cluster environment, implementing a stellar mass ratio of 2:1 with M200 = 9.5 × 1011 M⊙ for the more massive galaxy. Between the three different simulations, we varied the initial orbit of the infalling galaxies with respect to the cluster center. Results. We demonstrate that cluster environments are capable of stripping tidal dwarf galaxies from the host potential independently of the infall orbit of the merging galaxy pair, without instantly destroying the tidal dwarfs. Starting to evolve separately from their progenitor, these newly formed dwarf galaxies reach total masses of Mtot ≈ 107 − 9 M⊙ within the limits of our resolution. In the three tested orbit scenarios, we find three, seven, and eight tidal dwarf galaxies per merger, respectively, which survive longer than 1 Gyr after the merger event. Exposed to ram pressure, these gas dominated dwarf galaxies exhibit high star formation rates while also losing gas to the environment. Experiencing a strong headwind due to their motion through the intracluster medium, they quickly lose momentum and start spiraling towards the cluster center, reaching distances on the order of 1 Mpc from their progenitor. About 4 Gyr after the merger event, we still find three and four intact dwarf galaxies in two of the tested scenarios, respectively. The other stripped tidal dwarf galaxies either evaporate in the hostile cluster environment due to their low initial mass, or are disrupted as soon as they reach the cluster center. Conclusions. The dwarf production rate due to galaxy mergers is elevated when the interaction with a cluster environment is taken into account. Comparing their contribution to the observed galaxy mass function in clusters, our results indicate that ∼30% of dwarf galaxies in clusters could have been formed by stripping from galaxy mergers.