The PICS Project

Context. Planetary nebulae (PNe) and their luminosity function (PNLF) in galaxies have been used as a cosmic distance indicator for decades, yet a fundamental understanding is still lacking to explain the universality of the PNLF among different galaxies. So far, models for the PNLF have generally assumed near-solar metallicities and employed simplified stellar populations.Aims. In this work, we investigate how metallicity and helium abundances affect the resulting PNe and PNLF as well as the importance of the initial-to-final mass relation (IFMR) and circumnebular extinction in order to resolve the tension between PNLF observations and previous models.Methods. We introduce PICS (PNe In Cosmological Simulations), a PN model framework that takes into account the stellar metal-licity and is applicable to realistic stellar populations obtained from both cosmological simulations and observations. The framework combines current stellar evolution models with post-AGB tracks and PN models to obtain the PNe from the parent stellar population.Results. We find that metallicity plays an important role for the resulting PNe, as old metal-rich populations can harbor much brighter PNe than old metal-poor populations. In addition, we show that the helium abundance is a vital ingredient at high metallicities, and we explored the impact on the PNLF of a possible saturation of the helium content at higher metallicities. We present PNLF grids for different stellar ages and metallicities, where the observed PNLF bright end can be reached even for old stellar populations of 10 Gyr at high metallicities. Finally, we find that the PNLFs of old stellar populations are extremely sensitive to the IFMR, potentially allowing for the production of bright PNe.Conclusions. With PICS, we have laid the groundwork for studying how models and assumptions relevant to PNe affect the PNe and PNLF. Two of the central ingredients for the PNe and PNLF are the metallicity and helium abundance. Future applications of PICS include self-consistent modeling of PNe in a cosmological framework to explain the origin of the universality of the PNLF bright-end cutoff and using it as a diagnostic tool for galaxy formation.