# Low-redshift lowest-metallicity star-forming galaxies in the SDSS DR14

## TL;DR

This paper identifies 66 low-redshift, extremely low-metallicity star-forming galaxies from SDSS DR14, developing a new strong-line method for accurate metallicity measurement in such galaxies.

## Contribution

The paper introduces a new strong-line method tailored for precise metallicity determination in extremely low-metallicity galaxies, complementing existing methods.

## Key findings

- 66 candidate low-metallicity galaxies identified
- Developed a new strong-line metallicity estimation method
- Confirmed consistency among different abundance determination methods

## Abstract

We present a sample of low-redshift (z<0.133) candidates for extremely low-metallicity star-forming galaxies with oxygen abundances 12+logO/H<7.4 selected from the Data Release 14 (DR14) of the Sloan Digital Sky Survey (SDSS). Three methods are used to derive their oxygen abundances. Among these methods two are based on strong [OII]3727, [OIII]4959, and [OIII]5007 emission lines, which we call strong-line and semi-empirical methods. These were applied for all galaxies. We have developed one of these methods, the strong-line method, in this paper. This method is specifically focused on the accurate determination of metallicity in extremely low-metallicity galaxies and may not be used at higher metallicities with12+logO/H>7.5. The third, the direct Te method, was applied for galaxies with detected [OIII]4363 emission lines. All three methods give consistent abundances and can be used in combination or separately for selection of lowest-metallicity candidates. However, the strong-line method is preferable for spectra with a poorly detected or undetected [OIII]4363 emission line. In total, our list of selected candidates for extremely low-metallicity galaxies includes 66 objects.