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ALFALFA Discovery of the Most Metal-Poor Gas-Rich Galaxy Known: AGC 198691

, , , , , , , , , , , , , , and . (2016)cite arxiv:1603.03798Comment: 14 pages, 7 figures, 4 tables, accepted for publication in ApJ.

Abstract

We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength study of galaxies with HI masses in the range of 10$^6$-10$^7.2$~M$_ødot$ discovered by the ALFALFA survey. We have obtained spectra of the lone HII region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the temperature-sensitive OIII$łambda$4363 line and hence the determination of a "direct" oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 $\pm$ 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind HI survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.

Description

[1603.03798] ALFALFA Discovery of the Most Metal-Poor Gas-Rich Galaxy Known: AGC 198691

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