Whither or wither the Sulfur Anomaly in Planetary Nebulae?

Abstract

We present a thorough investigation of the long standing sulfur anomaly enigma. Our analysis uses chemical abundances from the most extensive dataset available for 126 planetary nebulae (PNe) with improved accuracy and reduced uncertainties from a 10x10 degree Galactic bulge region. By using argon as a superior PNe metallicity indicator, the anomaly is significantly reduced and better constrained. For the first time in PNe we show sulfur alpha-element lock-step with both oxygen and argon. We dispel hypotheses that the anomaly originates from underestimation of higher sulfur ionization stages. Using a machine learning approach, we show that earlier ionization correction factor (ICFs) schemes contributed significantly to the anomaly. We find a correlation between the sulfur anomaly and the age/mass of PNe progenitors, with the anomaly either absent or significantly reduced in PNe with young progenitors. Despite inherent challenges and uncertainties, we link this to PNe dust chemistry, noting those with carbon-dust chemistry show a more pronounced anomaly. By integrating these findings, we provide a plausible explanation for the residual, reduced sulfur anomaly and propose its potential as an indicator of relative galaxy age compositions based on PNe.