Towards precision cosmology with improved PNLF distances using VLT-MUSE. III. Impact of stellar populations in early-type galaxies

Distance measurements using the planetary nebula luminosity function (PNLF) rely on the bright-end cutoff magnitude (M^*), which is defined by a number of the planetary nebulae (PNe). In early-type galaxies (ETGs), the formation of these PNe is enigmatic; the population is typically too old to form the expected M^* PNe from single star evolution. We aim to provide a viable solution to this problem. We selected five ETGs with known MUSE-PNLF distances. The MUSE instrument allows us to calculate the PNLF and consistently investigate the underlying stellar populations. Using stellar population synthesis, we derived the population age, star formation history, metallicity, and alpha abundance. We compared these parameters to the PNLF variables: the absolute magnitude of the bright cutoff (M^*) and luminosity-specific PN number at the top 0.5 mag of the PNLF (α_0.5). We also compare our results with PNe In Cosmological Simulations (PICS) model applied to Magneticum Pathfinder analogue galaxies. The average mass-weighted ages and metallicities of the stellar populations in our datasets are typically old ($9 < Age < 13.5$ Gyr) and rather metal rich (-0.4 < M/H < +0.2). We find the value of M^* to be independent of age and metallicity in these ages and metallicity intervals. We observed a positive correlation between α_0.5 values and the mass fraction of stellar population ages of 2--10 Gyr, implying that most of the PNe originate from stars with intermediate ages. Similar trends are also found in the PICS analogue galaxies. We show that when ∼2% of the stellar mass present is younger than 10 Gyr, it is sufficient to form the M^* PNe in ETGs. We also present observing requirements for an ideal PNLF distance determination in ETGs.