  We have discovered a sample of 17 metal-poor, yet luminous, star-forming
galaxies at redshifts z~0.7. They were selected from the initial phase of the
DEEP2 survey of 3900 galaxies and the Team Keck Redshift Survey (TKRS) of 1536
galaxies as those showing the temperature-sensitive [OIII]l4363 auroral line.
These rare galaxies have blue luminosities close to L*, high star formation
rates of 5 to 12 solar masses per year, and oxygen abundances of 1/3 to 1/10
solar. They thus lie significantly off the luminosity-metallicity relation
found previously for field galaxies with strong emission lines at redshifts
z~0.7. The prior surveys relied on indirect, empirical calibrations of the R23
diagnostic and the assumption that luminous galaxies are not metal-poor. Our
discovery suggests that this assumption is sometimes invalid. As a class, these
newly-discovered galaxies are: (1) more metal-poor than common classes of
bright emission-line galaxies at z~0.7 or at the present epoch; (2) comparable
in metallicity to z~3 Lyman Break Galaxies but less luminous; and (3)
comparable in metallicity to local metal-poor eXtreme Blue Compact Galaxies
(XBCGs), but more luminous. Together, the three samples suggest that the
most-luminous, metal-poor, compact galaxies become fainter over time.
