Oxygen abundance distributions in six late-type galaxies based on SALT spectra of HII regions

TL;DR

This study measures oxygen abundances in H II regions of six late-type galaxies using SALT spectra, compares different methods, and examines their radial distributions to understand galaxy chemical composition.

Contribution

It provides new oxygen abundance measurements for six galaxies using the SALT telescope and compares multiple calibration methods, enhancing understanding of metallicity distributions.

Findings

Radial oxygen abundance distributions are consistent with surface brightness relations in four galaxies.

The 'counterpart' (C) method effectively estimates oxygen abundances in H II regions.

Surface brightness profiles can predict oxygen abundance distributions in galaxy disks.

Abstract

Spectra of 34 H II regions in the late-type galaxies NGC1087, NGC2967, NGC3023, NGC4030, NGC4123, and NGC4517A were observed with the South African Large Telescope (SALT). In all 34 H II regions, oxygen abundances were determined through the "counterpart" method (C method). Additionally, in two H II regions in which the auroral lines were detected oxygen abundances were measured through the classic Te method. We also estimated the abundances in our H II regions using the O3N2 and N2 calibrations and compared those with the C-based abundances. With these data we examined the radial abundance distributions in the disks of our target galaxies. We derived surface-brightness profiles and other characteristics of the disks (the surface brightness at the disk center and the disk scale length) in three photometric bands for each galaxy using publicly available photometric imaging data. The radial distributions of the oxygen abundances predicted by the relation between abundance and disk surface brightness in the W1 band obtained for spiral galaxies in our previous study are close to the radial distributions of the oxygen abundances determined from the analysis of the emission line spectra for four galaxies where this relation is applicable. Hence, when the surface-brightness profile of a late-type galaxy is known, this parametric relation can be used to estimate the likely present-day oxygen abundance in its disk.