J0811+4730: the most metal-poor star-forming dwarf galaxy known

TL;DR

This paper reports the discovery of J0811+4730, the most metal-poor star-forming galaxy known, with detailed spectroscopic analysis revealing its extremely low oxygen abundance and recent star formation activity.

Contribution

It presents the identification and detailed spectroscopic characterization of the most metal-poor star-forming galaxy, expanding understanding of low-metallicity galaxy properties.

Findings

Oxygen abundance of 12 + log O/H = 6.98, the lowest for a SFG

Galaxy's metallicity is ~10 times lower than similar luminosity SFGs

Significant recent star formation contributing to stellar mass

Abstract

We report the discovery of the most metal-poor dwarf star-forming galaxy (SFG) known to date, J0811+4730. This galaxy, at a redshift z=0.04444, has a Sloan Digital Sky Survey (SDSS) g-band absolute magnitude M_g = -15.41 mag. It was selected by inspecting the spectroscopic data base in the Data Release 13 (DR13) of the SDSS. LBT/MODS spectroscopic observations reveal its oxygen abundance to be 12 + log O/H = 6.98 +/- 0.02, the lowest ever observed for a SFG. J0811+4730 strongly deviates from the main-sequence defined by SFGs in the emission-line diagnostic diagrams and the metallicity - luminosity diagram. These differences are caused mainly by the extremely low oxygen abundance in J0811$+$4730, which is ~10 times lower than that in main-sequence SFGs with similar luminosities. By fitting the spectral energy distributions of the SDSS and LBT spectra, we derive a stellar mass of M* = 10^6.24 - 10^6.29 Msun (statistical uncertainties only), and we find that a considerable fraction of the galaxy stellar mass was formed during the most recent burst of star formation.