Testing For Azimuthal Abundance Gradients In M101

TL;DR

This study investigates the chemical abundance distribution in M101, finding marginal evidence for local deviations but no significant large-scale azimuthal gradients in oxygen abundance across the galaxy.

Contribution

The paper provides new spectroscopic data and analysis of oxygen abundance gradients, including detections of auroral lines and assessment of azimuthal variations in M101.

Findings

Local scatter in oxygen abundance is 0.15 dex in the west arc.

No significant large-scale azimuthal abundance variations detected.

Some regions show deviations from chemical homogeneity.

Abstract

New optical spectra of 28 H II regions in the M101 disk have been obtained, yielding 10 new detections of the [O III]{\lambda}4363 auroral line. The oxygen abundance gradient measured from these data, combined with previous observations, displays a local scatter of 0.15+/-0.03 dex along an arc in the west side of the galaxy, compared with a smaller scatter of 0.08+/-0.01 dex in the rest of the disk. One of the H I I regions in our sample (H27) has a significantly lower oxygen abundance than surrounding nebulae at a similar galactocentric distance, while an additional, relatively nearby one (H128) was already known to have a high oxygen abundance for its position in the galaxy. These results represent marginal evidence for the existence of moderate deviations from chemical abundance homogeneity in the interstellar medium of M101. Using a variety of strong-line abundance indicators, we find no evidence for significant large-scale azimuthal variations of the oxygen abundance across the whole disk of the galaxy.