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The Formation of Low-Mass Cluster Galaxies and the Universal Initial Galaxy Mass Function

Clusters of galaxies have an observed overdensity of low-luminosity systems in comparison with the field, although it is not yet agreed whether this effect is the result of initial galaxy mass functions that vary with environment or galaxy evolutionary effects. In this Letter, we argue that this overdensity is the result of low-mass systems with red colors that are overpopulating the faint end of the observed luminosity function in the nearby rich cluster Abell 0426. We show that the luminosity function of Abell 0426 becomes steeper, from the field value α = -1.25 ± 0.05 to α = -1.44 ± 0.04, because of a recently identified population of red low-mass cluster galaxies that are possibly the remnants of dynamically stripped high-mass systems. We further demonstrate, through simple models of stripping effects, how cluster luminosity functions can become artificially steep over time from the production of these low-mass cluster galaxies.