Abstract

Contributed Talk - Splinter StarClusters

Tuesday, 08 September 2026, 16:00   (MW-2050)

Extragalactic star clusters – their formation, stellar mass function, and evolution

Gerhard Hensler(1), Yannick Hein(1), Alessandro Boselli(2)
(1) Department of Astrophysics, University of Vienna, Austria; (2) Laboratoire d'Astrophysique de Marseille, France

Recent surveys of galaxy clusters allow the detection of both, star clusters (SCs) and star-free gas clouds, in the intra-cluster medium (ICM). For the origin of both types different processes are invoked, gas and stars dissolved by means of galaxy encounters or gas stripping thru the drag force acting on galaxies on their motion through the hot ICM. In the case of the tidal process SCs and even dwarf galaxies form in extended tails and both partly become freely floating. Another formation site are ram-pressure stripped (RPS) gas clouds. Both evolutionary paths are observationally manifested and appear in various facets. The physical processes of star formation under such astrophysically extreme conditions are an outstanding task of exploration, because it addresses a variety of fundamental actual questions on star-formation timescales: the dynamical effect of RPS on the star formation and its quenching, the initial mass function (IMF), the survival of dark clouds in the ICM, the removal of native gas clouds from the SCs, and their contribution to the escape of Lyman continuum (LyC) radiation. For these objectives we take advantage of the wealth of young SCs around the Virgo cluster spiral galaxy NGC 4254 detected in VESTIGE, the Virgo cluster H-alpha survey. 60 SCs are identified by the GALEX FUV with determined masses, ages, and separations from the mature galaxy. Only half of them are detected in H-alpha, because they have not yet lost their native gas clouds. CO observations are available with lower spatial resolution. In addition to masses and ages, we derive star-formation quenching timescales due to the gas evacuation, age-dependent escape fractions of LyC radiation, and expected variations of the upper-mass IMF at low star-formation rates. The variety of spectral brightness by the stellar mass sampling is investigated to constrain the number of massive stars. In addition to the astrophysical understanding of the cluster evolution, the study will deepen our insight into the formation of SCs in the early universe and their contribution to the re-ionization epoch and to the diffuse H-alpha emission in groups and clusters.