Planetary Nebulae in Face-On Spiral Galaxies. II. Planetary Nebula Spectroscopy

TL;DR

This study spectroscopically analyzed planetary nebulae in five face-on spiral galaxies to aid in dynamical mass measurements and explored spectral line ratios and extinction properties of PNe.

Contribution

It provides a comprehensive spectroscopic dataset of PNe in multiple galaxies and examines spectral line variations and extinction, aiding in understanding PNe populations and galaxy mass distribution.

Findings

[O III] and Balmer line ratios vary little across the luminosity function.

[N II] line strength increases with decreasing luminosity.

Typical circumstellar extinction is E(B-V) ~ 0.2, independent of luminosity.

Abstract

As the second step in our investigation of the mass-to-light ratio of spiral disks, we present the results of a spectroscopic survey of planetary nebulae (PNe) in five nearby, low-inclination galaxies: IC 342, M74 (NGC 628), M83 (NGC 5236), M94 (NGC 4736), and M101 (NGC 5457). Using 50 setups of the WIYN/Hydra and Blanco/Hydra spectrographs, and 25 observations with the Hobby-Eberly Telescope's Medium Resolution Spectrograph, we determine the radial velocities of 99, 102, 162, 127, and 48 PNe, respectively, to a precision better than 15 km/s. Although the main purpose of this data set is to facilitate dynamical mass measurements throughout the inner and outer disks of large spiral galaxies, our spectroscopy has other uses as well. Here, we co-add these spectra to show that to first order, the [O III] and Balmer line ratios of planetary nebulae vary little over the top ~1.5 mag of the planetary nebula luminosity function. The only obvious spectral change occurs with [N II], which increases in strength as one proceeds down the luminosity function. We also show that typical [O III]-bright planetaries have E(B-V) ~ 0.2 of circumstellar extinction, and that this value is virtually independent of [O III] luminosity. We discuss the implications this has for understanding the population of PN progenitors.