Abstract

Contributed Talk - Splinter GalaxyClusters

Wednesday, 09 September 2026, 16:45   (MW-1050)

Wendelstein Coma Cluster Census: Galaxy Luminosity Function and Structural Parameter Density Distributions

Raphael Zöller, Matthias Kluge, Ralf Bender, Jan-Niklas Pippert, Benjamin Seidel
University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München; Max Planck Institute for Extraterrestrial Physics

The galaxy luminosity function and the distribution of galaxy structural parameters in dense environments provide complementary probes of galaxy formation, the survival of low-mass dark matter subhalos, and the baryonic physics shaping cluster populations. We present a deep optical census of quenched resolved galaxies in the Coma cluster based on ≈1.5 deg² of u′-, g′-, and r′-band imaging around the cluster center obtained with the Wendelstein Wide Field Imager on the 2.1 m Fraunhofer Wendelstein Telescope. The data reach median 3σ surface-brightness limits in 10″ × 10″ boxes of 30.0, 29.6, and 28.7 mag arcsec⁻² in u′, g′, and r′, respectively, enabling a systematic characterization of the low-surface-brightness galaxy population. We measure structural parameters across a broad dynamic range in brightness, −24.5 g′ mag ≲ M ≲ −11.3 g′ mag, from the brightest cluster galaxy to low-luminosity dwarfs, including compact dwarf galaxies and ultra-diffuse galaxies. More than 6000 cluster member candidates are identified automatically based on their membership on the quiescent sequence in the u′ − g′ versus g′ − r′ color–color diagram. Structural parameters for bright galaxies are obtained through isophotal modeling, while faint galaxies are analyzed with fully automated parametric image fitting. Injection-recovery tests and two identically analyzed reference fields provide statistical corrections for completeness and contamination. Using this representative sample, we derive the g′-band galaxy luminosity function of quenched resolved galaxies in the Coma cluster, yielding a benchmark measurement that reliably probes the faint end. We report a best-fit single Schechter g′-band GLF with M* = −21.71(+0.26/-0.29) g′ mag, log₁₀(ϕ* [deg⁻² mag⁻¹]) = 1.355(+0.076/-0.079), and a comparatively steep faint-end slope α = −1.444 ± 0.015. A directly matched comparison with the Coma counterpart in SLOW, a constrained cosmological simulation using CDM, shows broad agreement between the GLFs down to the simulation limit of M = −15.5 g′ mag, despite a deficit of bright galaxies in the simulation. Finally, we construct completeness- and contamination-corrected number-density distributions in structural parameter space, specifically in the Re − μe, M − μe, and M − Re planes. These distributions provide a quantitative description of how galaxies populate structural parameter space across the full surface-brightness range, including the low-density low-surface-brightness tail. By moving beyond classical scatter plots and fitted linear scaling relations such as the Kormendy relation, this approach enables more direct and statistically robust comparisons with numerical simulations of galaxy populations. Together, the luminosity function and structural parameter relation number density measurements provide an observationally grounded framework for connecting the resolved galaxy population of a nearby massive cluster to simulations of cluster assembly and galaxy evolution.