Abundance determination of multiple star-forming regions in the HII galaxy SDSS J165712.75+321141.4

TL;DR

This study provides precise measurements of electron temperatures and ionic abundances in multiple star-forming regions of an HII galaxy, using spectrophotometry and tailored CLOUDY models, revealing similar evolutionary histories and radiation fields.

Contribution

It offers high-precision temperature and abundance measurements for multiple regions in an HII galaxy, along with detailed modeling and analysis of their star formation history and radiation characteristics.

Findings

Consistent electron temperatures and ionic abundances across regions.

CLOUDY models accurately reproduce observed ionic structures.

Similar star formation ages suggest interaction-triggered formation.

Abstract

We analyze high signal-to-noise spectrophotometric observations acquired simultaneously with TWIN, a double-arm spectrograph, from 3400 to 10400 \AA of three star-forming regions in the HII galaxy SDSS J165712.75+321141.4. We have measured four line temperatures: Te([OIII]), Te([SIII]), Te([OII]), and Te([SII]), with high precision, rms errors of order 2%, 5%, 6% and 6%, respectively, for the brightest region, and slightly worse for the other two. The temperature measurements allowed the direct derivation of ionic abundances of oxygen, sulphur, nitrogen, neon and argon. We have computed CLOUDY tailor-made models which reproduce the O2+ measured thermal and ionic structures within the errors in the three knots, with deviations of only 0.1 dex in the case of O+ and S2+ ionic abundances. In the case of the electron temperature and the ionic abundances of S+/H+, we find major discrepancies which could be consequence of the presence of colder diffuse gas. The star formation history derived using STARLIGHT shows a similar age distribution of the ionizing population among the three star-forming regions. This fact suggests a similar evolutionary history which is probably related to a process of interaction with a companion galaxy that triggered the star formation in the different regions almost at the same time. The hardness of the radiation field mapped through the use of the softness parameter $\eta$ is the same within the observational errors for all three regions, implying that the equivalent effective temperature of the radiation fields are very similar for all the studied regions of the galaxy, in spite of some small differences in the ionization state of different elements.