# Blueberry galaxies: the lowest mass young starbursts

## TL;DR

This paper identifies and characterizes a new class of very low-mass, metal-poor starburst galaxies at low redshift, called blueberry galaxies, which serve as local analogs to high-redshift Lyα emitters.

## Contribution

The study introduces a sample of 40 confirmed blueberry galaxies, revealing their properties and establishing them as the lowest mass, most metal-poor starburst galaxies known at low redshift.

## Key findings

- Blueberry galaxies are dwarf starburst galaxies with sizes less than 1 kpc.
- They exhibit very high ionization parameters, with [OIII]/[OII] ratios of 10-60.
- These galaxies have some of the lowest stellar masses and metallicities among starburst galaxies.

## Abstract

Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Ly$\alpha$ emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts ($z\lesssim0.05$) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at $z\lesssim0.05$ (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broad band colors, and studied their properties with MMT spectroscopy. From the whole SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. (An additional 7 candidates are contaminants, and 4 remain without spectra.) These blueberries are dwarf starburst galaxies with very small sizes ($< 1\hbox{kpc}$), and very high ionization ([OIII]/[OII]$\sim10-60$). They also have some of the lowest stellar masses ($\log(\hbox{M}/\hbox{M}_{\odot})\sim6.5-7.5$) and lowest metallicities ($7.1<12+\log(\hbox{O/H})<7.8$) starburst galaxies. Thus they are small counterparts to green peas and high redshift Ly$\alpha$ emitting galaxies.