The PICS Project: II. Circumnebular extinction variations and their effect on the planetary nebula luminosity function

TL;DR

This paper investigates the role of circumnebular extinction in shaping the planetary nebula luminosity function (PNLF) using the PICS framework. By implementing multiple extinction recipes derived from PN samples in the LMC and M31 and exploring metallicity dependence, the authors quantify how extinction modifies the bright-end cutoff across single stellar populations with ages from young to old. The key findings are that extinction can substantially dim the bright PNe in young populations, with an Optimized extinction recipe producing a near-constant cutoff around $M^*(5007) oughly -4.5$ for a range of ages, though older populations show smaller differences; moreover, the modeled extinctions underpredict the very high extinctions observed in nearby galaxies. The work highlights the need for improved circumnebular dust evolution modeling and more extensive, unbiased PN extinction measurements to reconcile theory with extragalactic PN populations.

Abstract

For decades, the theoretical understanding of planetary nebulae (PNe) has remained in tension with the observed universal bright-end cutoff of the PN luminosity function (PNLF). The brightest younger PN populations have been observed to be fainter in their [O III] emission than expected. Recent studies have proposed that circumnebular extinction is a key ingredient in bringing their brightness down to the observed level. In this work we use the recently introduced PICS (PNe In Cosmological Simulations) framework to investigate the impact of different circumnebular extinction treatments on the modeled PNe and their PNLF for a large range of stellar ages and metallicities. We test how different slopes in the observed relation of extinction versus central star mass modify the bright-end cutoffs of the PNLF, finding that steeper slopes lead to large changes for young stellar populations. In contrast, the differences for older PNe are much smaller. However, for individual PNe, the extinctions observed in nearby galaxies appear to be much higher than the models predict, showing that improvements on both the modeling and observational sides are needed to gain a better understanding of the brightest and strongly extincted PNe. These findings further advance the theoretical foundation for interpreting observed extragalactic PN populations coming from more complex composite stellar populations in the future.

Figures (4)

• Figure 1: Circumnebular extinction of [O iii], $A_{5007}$, as a function of post-AGB time of the central star for the different extinction recipes tested. The recipes are based on the relations by jacobyciardullo25 for the extinction $c(\mathrm{H}\beta)$ versus core mass for the brightest PNe in M 31 and the LMC. The colors indicate the Combined (blue), LMC (green), M 31 (orange), and Optimized (purple) fits, and the line styles denote the respective OR (solid), shifted OR (dotted), and OLS (dash-dotted) fits for all but Optimized. The dotted OR fit + 0.08 lines are based on their OR relations shifted by $\Delta c(\mathrm{H}\beta) = +0.08$.
• Figure 2: Circumnebular extinction of $\mathrm{H}\beta$, $c(\mathrm{H}\beta)$, as a function of stellar final mass for the brightest observed and modeled PNe assuming different extinction recipes. LMC-like PNe ($Z=0.007$) are shown on the left and M 31-like PNe ($Z=0.015$) on the right. Bright PNe are selected according to $M(5007) \leq -3.5$, analogously to the observed PNe (black circles) as selected by jacobyciardullo25. The lines indicate the medians and the shaded regions the $1\sigma$-scatter of the extinction values at the respective final masses. The extinction recipes correspond to the input fit relations from jacobyciardullo25, orthonormal regression (OR), shifted OR by $\Delta c(\mathrm{H}\beta) = +0.08$, and ordinary least squares (OLS).
• Figure 3: Grid of SSP PNLFs for different metallicities (columns; $Z=0.001$, 0.01, 0.02, 0.04, 0.08) and ages (rows; $t_\mathrm{age} = 0.25$ to 13G for the different circumnebular extinction recipes tested (colored lines), as well as without extinction (dashed black lines). The observed universal bright-end cutoff of $M(5007) = -4.5$ is indicated by the dashed gray lines.
• Figure 4: Circumnebular extinction of [O iii], $A_{5007}$, versus the intrinsic de-reddened [O iii] magnitude, $M_\mathrm{dered}(5007)$, of observed and modeled PNe for three different circumnebular extinction recipes. Left: Combined OR. Middle: Combined OR with a shift of $\Delta c(\mathrm{H}\beta) = +0.08$. Right: Combined OR with the same shift of +0.08 and an added normally distributed scatter in $c(\mathrm{H}\beta)$ of $\sigma = 0.1$. The values of the observed PNe are taken from davis+18, who observed PNe in the bulge of M 31 and compiled the data from other works for three other galaxies: the LMC reidparker10, NGC 4697 mendez+05, and NGC 5128 walsh+12. The dashed gray lines indicate the bright-end cutoff of the PNLF of $M(5007) = -4.5$.