Planetary nebulae as tracers of stellar population properties: a pilot study with MUSE

TL;DR

This work leverages DELF-enabled integral-field spectroscopy with MUSE to detect planetary nebulae in the bright centers of ten early-type galaxies and to connect PN statistics with spatially resolved stellar population properties. By measuring the α-parameter and the PNLF while deriving ages and metallicities from pPXF/GIST analyses, the study finds a metallicity-driven correlation with the PN population and a weak dependence on age, alongside a robust anti-correlation with FUV excess. The results support the use of PNe as tracers of underlying stellar populations and halo structure, while highlighting limitations of archival data and the need for larger, deeper, and higher-resolution surveys (e.g., AO, BlueMUSE) to refine the PN–population relations. Overall, the paper demonstrates the feasibility of co-detecting PNe and measuring stellar properties in galaxy centers, enabling more precise calibrations of PN-based tracers for galaxy evolution studies, and providing a framework for future, higher-sensitivity investigations.

Abstract

Planetary nebulae (PNe) are the only single stars in galaxies outside the Local Group that can be used as kinematic tracers of the diffuse light in the extended halo. Analysing their luminosity-specific number density across galaxies of different morphologies has also shown hints that they may be used as tracers of the age and metallicity of stellar populations. A proper understanding of this relation has been hindered by the fact that simultaneously detecting PNe and accurately measuring stellar properties is extremely difficult using classical narrow-band imaging methods, which cannot detect PNe in the bright centres of galaxies. In this work, we use integral-field spectroscopy to overcome this challenge, analysing the inner regions of a sample of ten early-type galaxies from the Extended Planetary Nebulae Survey (ePN.S) for which archival MUSE data was available. With the Diffuse Emission-Line Filter (DELF) technique, we automate the detection of PNe, and perform spectral fitting on the diffuse light to infer kinematics and stellar population parameters. We compare the PN number density profile and its associated alpha-parameter with multiple properties of the host galaxies. We find that our sample follows the previously observationally constrained correlation with the metallicity of the host galaxy. We find a weak anti-correlation between the alpha-parameter and the FUV excess, highlighting the possible relation between the visibility lifetime of PNe on the spectral energy distribution of their host galaxies, with fewer PNe detected in association with stellar populations characterized by a UV excess.

Figures (70)

• Figure 1: Flowchart describing the method used to perform the analysis carried out in this paper.
• Figure 2: Kinematic properties of the stellar component of NGC 1387 as obtained with GIST.
• Figure 3: Age and metallicity of the stellar component of NGC 1387 as obtained with GIST.
• Figure 4: Full MUSE spectrum for one of the sources classified as PNe in NGC 1387. A pink vertical line indicates the position of the [OIII line].
• Figure 5: Zoom-in on the region of the [Oiii] line using the spectra constructed from the aperture photometry method described in the text. A grey vertical line indicates the restframe wavelength in air of the [Oiii] line.