Combined with the Balmer-derived star formation rates (SFRs), these galaxies have average inverse SFR/M⋆ of ≈100 Myr. We determine that these metal-poor galaxies have low stellar masses, M⋆ ≈108.1–109.5M⊙. By modelling infrared and optical photometry, we derive stellar masses and other stellar properties. We present results from deep Spitzer/Infrared Array Camera (IRAC) observations of 28 metal-poor, strongly star-forming galaxies selected from the DEEP2 Galaxy Survey. Finally, we study the dependence on age of the buildup of metals and the emission-line strength. We investigate the evolution of H β using both instantaneous and continuous starburst models, finding that XMPGs are best characterized by continuous starburst models. We also improve upon the metallicities for two other XMPGs from previous work. Using the robust direct T e method, we identify eight new extremely metal-poor galaxies (XMPGs) with 12 + log O/H ≤7.65, including one at 6.949 ± 0.091, making it the lowest-metallicity galaxy reported to date at these redshifts. Using a Keck/DEIMOS spectral database of about 18,000 galaxies between z = 0.2 and z = 1, we search for such extreme emission-line galaxies with the goal of determining their metallicities.
Galaxies with strong emission lines and high equivalent widths (rest-frame EW(H β ) ≳ 30 Å) are ideal candidates for the lowest-metallicity galaxies to z ∼ 1. Low-metallicity galaxies may provide key insights into the evolutionary history of galaxies.
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