Direct Method Gas Phase Oxygen Abundances of 4 Lyman Break Analogs

TL;DR

This paper measures gas-phase oxygen abundances in 4 Lyman Break Analogs using direct methods, confirming their status as low-metallicity outliers and discussing potential biases in empirical estimates due to excitation conditions.

Contribution

It provides direct oxygen abundance measurements for LBAs, validating their low metallicity status and examining biases in empirical methods due to excitation anomalies.

Findings

Direct abundances align with empirical estimates.

LBAs are low-metallicity outliers in the MZ relation.

Star formation and low metallicity support the FMR prediction.

Abstract

We measure the gas-phase oxygen abundances in 4 Lyman Break Analogs (LBAs) using auroral emission lines to derive direct abundances. The direct method oxygen abundances of these objects are generally consistent with the empirically-derived strong-line method values, confirming that these objects are low oxygen abundance outliers from the Mass-Metallicity (MZ) relation defined by star forming SDSS galaxies. We find slightly anomalous excitation conditions (Wolf-Rayet features) that could potentially bias the empirical estimates towards high values if caution is not exercised in the selection of the strong-line calibration used. The high rate of star formation and low oxygen abundance of these objects is consistent with the predictions of the Fundamental Metallicity Relation (FMR), in which the infall of relatively unenriched gas simultaneously triggers an episode of star formation and dilutes ISM of the host galaxy.