Strong [OIII]{\lambda}5007 emission line compact galaxies in LAMOST DR9: Blueberries, Green Peas and Purple Grapes

TL;DR

This study analyzes 1547 compact galaxies with strong [OIII]{ extlambda}5007 emission from LAMOST DR9, classifying them into Blueberries, Green Peas, and Purple Grapes, and investigates their properties, metallicity, and environment.

Contribution

It provides a large sample analysis of strong [OIII]{ extlambda}5007 emission line compact galaxies, classifies them into three groups, and explores their physical properties and metallicity relations.

Findings

SFR increases with redshift and mass within the same redshift bin.

Galaxies have median metallicity of 8.10, below the mass-metallicity relation.

Most galaxies are in less dense environments.

Abstract

Green Pea and Blueberry galaxies are well-known for their compact size, low mass, strong emission lines and analogs to high-z Ly{\alpha} emitting galaxies. In this study, 1547 strong [OIII]{\lambda}5007 emission line compact galaxies with 1694 spectra are selected from LAMOST DR9 at the redshift range from 0.0 to 0.59. According to the redshift distribution, these samples can be separated into three groups: Blueberries, Green Peas and Purple Grapes. Optical [MgII]{\lambda}2800 line feature, BPT diagram, multi-wavelength SED fitting, MIR color, and MIR variability are deployed to identify 23 AGN candidates from these samples, which are excluded for the following SFR discussions. We perform the multi-wavelength SED fitting with GALEX UV and WISE MIR data. Color excess from Balmer decrement shows these strong [OIII]{\lambda}5007 emission line compact galaxies are not highly reddened. The stellar mass of the galaxies is obtained by fitting LAMOST calibrated spectra with the emission lines masked. We find that the SFR is increasing with the increase of redshift, while for the sources within the same redshift bin, the SFR increases with mass with a similar slope as the SFMS. These samples have a median metallicity of 12+log(O/H) of 8.10. The metallicity increases with mass, and all the sources are below the mass-metallicity relation. The direct-derived Te-based metallicity from the [OIII]{\lambda}4363 line agrees with the empirical N2-based empirical gas-phase metallicity. Moreover, these compact strong [OIII]{\lambda}5007 are mostly in a less dense environment.