Outliers from the Mass--Metallicity Relation I: A Sample of Metal-Rich Dwarf Galaxies from SDSS

TL;DR

This study identifies 41 low-mass, high-oxygen abundance outliers from the galaxy mass-metallicity relation, suggesting they are transitional dwarf galaxies nearing the end of star formation, with typical star formation rates and isolated morphologies.

Contribution

It presents a new sample of metal-rich dwarf galaxies that deviate from the typical mass-metallicity relation, providing insights into their nature and evolutionary stage.

Findings

41 outliers with high oxygen abundance identified

These galaxies are isolated with typical star formation rates

They are likely transitional dwarf galaxies nearing star formation end

Abstract

We have identified a sample of 41 low-mass high--oxygen abundance outliers from the mass--metallicity relation of star-forming galaxies measured by Tremonti et al (2004). These galaxies, which have 8.6 < [12 + log(O/H)] < 9.3 over a range of -14.4 > M_B > -19.1 and 7.4 < log M_*/M_solar < 10, are surprisingly non-pathological. They have typical specific star formation rates, are fairly isolated and, with few exceptions, have no obvious companions. Morphologically, they are similar to dwarf spheroidal or dwarf elliptical galaxies. We predict that their observed high oxygen abundances are due to relatively low gas masses, concluding that these are transitional dwarf galaxies nearing the end of their star formation activity.