Quantum mechanics

Biology

Galaxy

Computer security

Lambda

Fishery

RADIUS

Astrophysics

Computer science

Observable

Physics

Electron temperature

Ionization

Mathematics

Optics

Abundance (ecology)

Effective radius

Geometry

Nebula

Electron

Stars

Line (geometry)

Spiral galaxy

The Astrophysical Journal

The chemical abundances of spiral galaxies, as probed by H ii regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 H ii regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual H ii regions. We find that the dispersion in <?CDATA ${T}_{e}-{T}_{e}$?> relationships is dependent on ionization, as characterized by <?CDATA ${F}_{\lambda 5007}/{F}_{\lambda 3727}$?> , and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that [N ii ] and [S iii ] provide the most robust measures of electron temperature in low-ionization zones, while [O iii ] provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of <?CDATA ${\alpha }_{{\rm{N}}/{\rm{O}}}=-0.33$?> dex/ R e with σ tot. = 0.08 for R g / R e &lt; 2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O–O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich H ii regions.

CHAOS IV: Gas-phase Abundance Trends from the First Four CHAOS Galaxies