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

Abstract

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 LBT/MODS spectra of 52 H II regions in NGC3184 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 the dispersion in T e − T e relationships is dependent on ionization, as characterized by F λ5007 /F λ3727 , and so 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 highionization 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 IFU studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of α N/O = −0.33 dex/R e with σ tot. = 0.08 for R g /R e < 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. Spectral ReductionsFor a detailed description of the data reduction procedures we refer the reader to (B15). Here, we only note the primary points of our data processing. Spectra were reduced and analyzed using the beta-version of the MODS reduction pipeline 1 which runs within the XIDL 2 reduction package. Given that the bright disks of CHAOS galaxies can complicate local sky subtraction, 1

CHAOS VI: Direct Abundances in NGC 2403

“…We then use all available temperature data within an Hii region to obtain a weighted average temperature within each ionization zone. We re-derive the oxygen abundances of all CHAOS galaxies using this new temperature prioritization method, and we find that the gradients are consistent with the results of Berg et al (2020). For NGC 2403, we measure a direct oxygen abundance gradient of −0.09(±0.03) dex/R e , with an intrinsic dispersion of 0.037(±0.017) dex, and an N/O abundance gradient of −0.17(±0.03) dex/R e with an intrinsic dispersion of 0.060(±0.018) dex.…”

The diffuse ionized gas (DIG) in star-forming galaxies: the influence of aperture effects on local H ii regions

“…(Pilyugin et al 2012). The recent catalog of H spectra of the CHAOS project (Berg et al 2015;Croxall et al 2015Croxall et al , 2016Berg et al 2020) is often used because of its high S/N ratio, large spectral coverage, homogeneity, and number of targets. This catalog is based of high-quality LBT observations of about 200 H regions in three galaxies (NGC628, M51, and M101), between 7.2 Mpc and 9.8 Mpc, for which the 1 slit width samples ∼35-45pc.…”

A geostatistical analysis of multiscale metallicity variations in galaxies [I]: Introduction and comparison of high-resolution metallicity maps to an analytic metal transport model

“…Most local spiral galaxies have negative metallicity gradients (e.g. Searle 1971;Vila-Costas & Edmunds 1992;Zaritsky et al 1994;Berg et al 2013Berg et al , 2020Ho et al 2015;Belfiore et al 2017;Poetrodjojo et al 2018), consistent with inside-out star formation (Boissier & Prantzos 1999). It is still an open question whether these metallicity gradients are produced by global galaxy properties such as stellar mass (Ho et al 2015;Belfiore et al 2017), or by small-scale versions of well-known galaxy scaling relations, such as the local mass-metallicity relation (Rosales-Ortega 2013;Erroz-Ferrer et al 2019).…”