Chemical abundances in the dwarf galaxy NGC 4163 based on the nebular and auroral emission lines by I. A. Zinchenko et al. on Wednesday 30 November

We constructed an oxygen abundance map and N/O ratio map of the unusually low

excitation dwarf irregular galaxy NGC 4163 based on publicly available

spectroscopy obtained by the MaNGA survey. We detected auroral emission line

[OII]$\lambda\lambda$7320,7330 which allows us to measure chemical abundance by

direct T$_e$ method. We found that the scatter of the oxygen abundance derived

by the strong line method is large. The oxygen abundances 12 + log(O/H) derived

by strong line method vary from ~7.3 to ~7.8 with a mean value of ~7.55. The

oxygen abundances derived in two apertures of 2 arcseconds by the direct T$_e$

method using our measurements of the O$^+$ auroral line is about 7.8 dex. The

nitrogen-to-oxygen ratio log(N/O) of about -1.5 is typical value for a low

metallicity galaxy, maybe slightly shifted towards higher N/O ratios with

respect to the N/O values in the HII regions in nearby galaxies. An unusual

negative trend between log(N/O) and oxygen abundance is detected. NGC 4163 is a

gas-poor galaxy with a neutral atomic gas mass fraction of around 0.25. The

oxygen abundance in the galaxy is only around 0.1 of the oxygen abundance

potentially attainable in a galaxy with such a gas mass fraction. The low

metallicity coupled with the low gas mass fraction implies that either the

metallicity of the interstellar medium of the galaxy was reduced by pristine

gas infall in the recent epoch or the evolution of this galaxy was accompanied

by strong galactic winds.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15710v1