Analysis of metal-poor galaxy spectra in the redshift range 0.00574-0.05368

TL;DR

This study models the spectra of extremely metal-poor galaxies at low redshift, considering various physical scenarios, to classify galaxy types and analyze element abundance trends, revealing insights into nitrogen and oxygen formation processes.

Contribution

It introduces a comprehensive modeling approach using the { extsc{suma}} code to classify metal-poor galaxies and analyze element abundance trends, including merging galaxy identification.

Findings

Five galaxies are identified as merging systems.

Oxygen abundances are generally below solar levels.

Nitrogen-to-oxygen ratios reveal formation processes.

Abstract

We present an analysis of the metal-poor galaxy spectra in the redshift range 0.00574$\leq$z$\leq$0.05368 which were reported by Nakajima et al (2022) in their EMPG (extreme metal poor galaxy) sample. The models account for the active galactic nuclei (AGN) and the starburst (SB) galaxies, for accretion and ejection, for the physical parameters and the element abundances. The results are obtained in particular for the two cases, the emitting nebula is ejected outward from the galaxy radiation source (RS) and the emitting nebula is accreted towards the RS. We adopt the code {\sc suma} which allows to choose the direction of the clouds relative to the RS. The modelling results which reproduce a single galaxy spectrum with the highest precision allow to classify this object as an AGN ejecting, an AGN accreting, an SB ejecting or an SB accreting type. When more models are equally valid we suggest that the galaxy is the product of merging. Our results show that among the eleven sample galaxies five are such. We focus on the N/O trends with the oxygen metallicity and with the redshift to identify the nitrogen/oxygen relative formation processes and the process-rates, respectively, for intermediate-mass stars. Our results show that O/H relative abundances calculated for the sample galaxies are lower than solar by a factor $\leq$5. Yet, a few values were found above solar. He/H were calculated lower than solar by factors $\leq$ 100 and N/H by factors $\leq$135.