Emission spectrum of ionized gas in the Irr galaxy Holmberg II

TL;DR

This study analyzes the emission spectrum of ionized gas in Holmberg II, estimating elemental abundances and comparing metallicity estimation methods to identify the most reliable techniques for irregular galaxies.

Contribution

It provides detailed abundance measurements and evaluates the accuracy of various metallicity estimation methods in irregular galaxy HII regions.

Findings

Average metallicity Z=0.1 or 0.3 Zsun depending on the method

Most methods confirm systematic deviations in metallicity estimates

Identification of the most reliable techniques for Irr galaxy analysis

Abstract

We study the ionized gas spectrum of star forming regions in the Holmberg II galaxy using the optical long-slit spectroscopic observations made at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). We estimate the oxygen, nitrogen, sulphur, neon, and argon abundances in individual HII regions and find the average metallicity in the galaxy to be Z=0.1 or 0.3 Zsun depending on the estimation method employed. We use these observations combined with the results of our earlier studies of the Irr galaxy IC 10 and BCD galaxy VII Zw 403 to compare the currently most popular methods of gas metallicity estimation in order to select among them the techniques that are most reliable for analysing Irr galaxies. To this end, we use the "direct" Te method and six empirical and theoretical methods. The results of our observations mostly confirm the conclusions of Lopez-Sanchez et al. (2012) based on the analysis of systematic deviations of metallicity estimates derived by applying different methods to "model" HII regions.