ALFALFA DISCOVERY of the MOST METAL-POOR GAS-RICH GALAXY KNOWN: AGC 198691

A.S. Hirschauer, J.J. Salzer, E.D. Skillman, D. Berg, K.B.W. McQuinn, J.M. Cannon, A.J.R. Gordon, M.P. Haynes, R. Giovanelli, E.A.K. Adams, Steven Janowiecki, K.L. Rhode, R.W. Pogge, K.V. Croxall, E. Aver

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Abstract

© 2016. The American Astronomical Society. All rights reserved. We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of H I in Extremely Low-Mass Dwarfs project, which is a multi-wavelength study of galaxies with H I masses in the range of 106-107.2 M?, discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph 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 [O III]?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 ± 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 H I survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.
Original languageEnglish
JournalThe Astrophysical Journal
Volume822
Issue number2
DOIs
Publication statusPublished - 2016

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