Spectroscopic Observations of Planetary Nebulae in the Northern Spur of M31

TL;DR

This study uses spectroscopic data of planetary nebulae in M31's Northern Spur to analyze their chemical compositions, providing insights into the galaxy's substructure formation and possible tidal debris origins.

Contribution

First spectroscopic analysis of PNe in M31's Northern Spur linking chemical abundances to galaxy substructure origins.

Findings

Detection of [O III] 4363 line enabling temperature measurements.

Variation in oxygen abundance suggesting a connection to tidal debris.

Support for the Northern Spur being linked to the Southern Stream.

Abstract

We present spectroscopy of three planetary nebulae (PNe) in the Northern Spur of the Andromeda Galaxy (M31) obtained with the Double Spectrograph on the 5.1 m Hale Telescope at the Palomar Observatory. The samples are selected from the observations of Merrett et al. Our purpose is to investigate formation of the substructures of M31 using PNe as a tracer of chemical abundances. The [O III] 4363 auroral line is detected in the spectra of two objects, enabling temperature determinations. Ionic abundances are derived from the observed collisionally excited lines, and elemental abundances of nitrogen, oxygen, and neon as well as sulphur and argon are estimated. Correlations between oxygen and the alpha-element abundance ratios are studied, using our sample and the M31 disk and bulge PNe from the literature. In one of the three PNe, we observed relatively higher oxygen abundance compared to the disk sample in M31 at similar galactocentric distances. The results of at least one of the three Northern Spur PNe might be in line with the proposed possible origin of the Northern Spur substructure of M31, i.e. the Northern Spur is connected to the Southern Stream and both substructures comprise the tidal debris of the satellite galaxies of M31.