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]λ4363 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.
Bibliographical noteFunding Information:
J.J.S. and A.S.H. received financial support from the College of Arts and Sciences of Indiana University that helped to enable this work. The ALFALFA team at Cornell is supported by NSF grants AST-0607007 and AST-1107390 to R.G. and M.P.H. and by a grant from the Brinson Foundation. J.M.C. is supported by NSF grant AST-1211683. This work was supported in part by NASA through grant GO-13750 from the Space Telescope Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.
- galaxies: ISM
- galaxies: abundances
- galaxies: dwarf
- galaxies: evolution
- galaxies: star formation