Metal-Rich PNe in the Outer Reaches of M31
Bruce Balick, Karen Kwitter, Romano Corradi, Richard Henry

TL;DR
This study analyzes the metallicity, distribution, and origins of metal-rich planetary nebulae in the outer regions of M31, revealing a flat metallicity gradient and suggesting a starburst event about 2 billion years ago.
Contribution
It provides new spectroscopic data on distant PNe in M31 and demonstrates their uniform solar-like metallicity and disk-like kinematics, challenging previous assumptions about their origins.
Findings
O/H is uniformly solar-like in all 18 PNe studied.
The PNe distribution and kinematics resemble M31's disk more than its halo.
The O/H gradient is surprisingly flat beyond 30 kpc.
Abstract
Spectroscopic data of two relatively [O III]-luminous-PNe have been obtained with the 10.4-m Gran Telescopio Canarias. M174 and M2496 are each ~1 degree from the center of M31 along opposite sides of its minor axis. The ensemble of these two distant PNe plus 16 similarly luminous outer-disk PNe published earlier (Kwitter et al. 2012 & 2013) forms a homogeneous group in luminosity, metal content, progenitor mass, age, and kinematics. The main factual findings of our work are: (1) O/H (and other low-mass alpha elements and their ratios to O) is uniformly solar-like in all 18 PNe <12+log(O/H)> = 8.62 +/- 0.14); (2) the general sky distribution and kinematics of the ensemble much more closely resemble the rotation pattern of the classical disk of M31 than its halo or bulge; (3) the O/H gradient is surprisingly flat beyond R_g ~30 kpc, and may be flat throughout the entire range of R_g…
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Taxonomy
TopicsAdvanced NMR Techniques and Applications
