Andromeda IV: a new Local Volume very metal-poor galaxy

TL;DR

Andromeda IV is a newly identified, extremely metal-poor, gas-rich dwarf galaxy in the Local Volume, with spectroscopic analysis confirming its low metallicity and contributing to understanding of chemical evolution in low-surface brightness galaxies.

Contribution

This study provides the first spectroscopic metallicity measurements of Andromeda IV, establishing it as a new example of an extremely metal-deficient galaxy in the Local Volume.

Findings

O/H values of 7.49 and 7.55 from spectroscopic analysis.

And IV's metallicity aligns with the standard O/H-L_B relation for dwarf irregular galaxies.

The galaxy exhibits a large diversity in HI mass, challenging simple chemical evolution models.

Abstract

And IV is a low-surface brightness (LSB) dwarf galaxy at the distance of 6.1 Mpc, projecting close to M 31. In this paper the results of spectroscopy of And IV the two brightest HII regions with the SAO 6-m telescope (BTA) are presented. In both of them the faint line [OIII]4363 was detected that allowed us to determine their O/H by the classical T_e method. Their values of 12+log(O/H) are equal to 7.49+-0.06 and 7.55+-0.23, respectively. The comparison of these direct O/H determinations with the two most reliable semi-empirical and empirical methods shows their good consistency. For And IV absolute blue magnitude of M_B=-12.6, our value of O/H corresponds well to the `standard' relation between O/H and L_B for dwarf irregular galaxies (DIGs). And IV appears to be a new representative of the extremely metal-deficient gas-rich galaxies in the Local Volume. The very large range of M(HI) for LSB galaxies with close metallicities and luminosities indicates that the simple models of LSBG chemical evolution are too limited to predict such striking diversity.