# The resolved chemical composition of the starburst dwarf galaxy CGCG007-025: Direct method versus photoionization model fitting

**Authors:** Vital Fernández, Ricardo Amorín, Rubén Sanchez-Janssen, Macarena Garcia del Valle-Espinosa, Polychronis Papaderos  
**arXiv:** [2212.10593](https://arxiv.org/abs/2212.10593)  
**Date:** 2022-12-20  
**Summary page:** https://www.summarizepaper.com/en/paper/2212.10593v1/

## Key points

- Gas chemical composition of the starburst dwarf galaxy CGCG007-025 is the focus of this work
- Spatial behavior observed using VLT/MUSE instrument
- New line measurement library allows analysis of almost 7800 voxels in the galaxy
- Analysis based on direct method, measuring emission lines to derive elemental abundances
- Direct method analysis only possible for 484 voxels with good detection of $[SIII]$6312$\mathring{\mathrm{A}}$ temperature diagnostic line
- Population synthesis technique used to correct for stellar absorption
- Neural networks utilized to fit photoionization models
- Ionic abundances show spatially normal distribution with a standard deviation of approximately 0.1 dex
- Oxygen abundance distribution found to be $12+\log(O/H)=7.88\pm0.11$, indicating relatively low levels compared to hydrogen
- Temperature and electron density exhibit normal distributions across the galaxy, but central region has higher electron density than average
- Extinction measurements and ionization parameter ($log(U)$) also show spatial variations
- Correlation between ionization state and sulfur ions' distribution observed
- Discrepancies between direct method and photoionization model results discussed, with recommendation to overestimate minimum flux uncertainty

## Summary

This work focuses on the gas chemical composition of the starburst dwarf galaxy CGCG007-025. The galaxy is currently undergoing a galaxy-wide burst of star formation, and its spatial behavior has been observed using the VLT/MUSE instrument. In this study, the authors present a new line measurement library that allows them to analyze almost 7800 voxels in the galaxy. The analysis of the gas chemical composition is primarily based on the direct method, which involves measuring emission lines from different ions and using them to derive elemental abundances. However, due to limitations in detection, the direct method analysis is only possible for 484 voxels with good detection of the $[SIII]$6312$\mathring{\mathrm{A}}$ temperature diagnostic line. To account for stellar absorption, which can affect the measured recombination fluxes, a population synthesis technique is employed to correct for this effect. Additionally, the authors discuss a new algorithm that utilizes neural networks to fit photoionization models. The results of the analysis reveal that the ionic abundances show a spatially normal distribution with a standard deviation ($\sigma$) of approximately 0.1 dex. Only half of this variation can be attributed to uncertainties in the measurements. The oxygen abundance distribution is found to be $12+\log(O/H)=7.88\pm0.11$, indicating relatively low levels of oxygen compared to hydrogen. The temperature ($T_{e}[SIII]$) and electron density ($ne[SII]$) also exhibit normal distributions across the galaxy; however, in its central and brightest region $ne[SII]$ is nearly three times higher than its mean value for its entire galaxy. This discrepancy is also reflected in extinction measurements as well as in its ionization parameter ($log(U)$), which characterizes degree of ionization within a region and shows a distribution of $-2.52^{+0.17}_{-0.19}$. This parameter's spatial behavior agrees with that seen in its $S^{2+}/S^{+}$ map indicating correlation between ionization state and sulfur ions' distribution throughout it . Finally, discrepancies between results obtained through direct method and those obtained by fitting photoionization models are discussed by authors who recommend overestimating minimum flux uncertainty by one order below maximum line flux uncertainty as way to improve agreement with former technique . Overall , this study provides detailed insights into resolved chemical composition of CGCG007-025 during its starburst phase highlighting spatial variations in elemental abundances , temperature , electron density , extinction , and ionization state within it .