Uncovering Blue Diffuse Dwarf Galaxies
Bethan L. James, Sergey Koposov, Daniel P. Stark, Vasily Belokurov,, Max Pettini, and Edward W. Olszewski

TL;DR
This study identifies a new class of faint, blue, diffuse dwarf galaxies with extremely low metallicities, using morphology-based search methods on SDSS images, revealing their active star formation and potential link to other dwarf galaxy types.
Contribution
It introduces a novel morphology-based search technique to find diffuse, metal-poor dwarf galaxies overlooked by traditional emission-line methods.
Findings
Eight galaxies have oxygen abundances between 7.45 and 8.0.
Two galaxies are classified as extremely metal-poor (XMPs).
All galaxies show active star formation with young stellar populations.
Abstract
Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a sub-sample of galaxies that were selected via a morphology-based search on SDSS images with the aim of finding these elusive XMP galaxies. By using the recently discovered extremely metal-poor galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated HII regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ~100 of these blue, diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45<12+log(O/H)<8.0, with two galaxies being classified…
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Taxonomy
TopicsAstronomy and Astrophysical Research · Galaxies: Formation, Evolution, Phenomena · Stellar, planetary, and galactic studies
