Search for: All records

Abstract Low-metallicity galaxies may provide key insights into the evolutionary history of galaxies. 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. 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. 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. We also improve upon the metallicities for two other XMPGs from previous work. We investigate the evolution of H β using both instantaneous and continuous starburst models, finding that XMPGs are best characterized by continuous starburst models. Finally, we study the dependence on age of the buildup of metals and the emission-line strength. 

We present a search for extreme emission line galaxies (EELGs) atz< 1 in the COSMOS and North Ecliptic Pole (NEP) fields with imaging from Subaru/Hyper Suprime-Cam (HSC) and a combination of new and existing spectroscopy. We select EELGs on the basis of substantial excess flux in thezbroad band, which is sensitive to Hαat 0.3 ≲z≲ 0.42 and [Oiii]λ5007 at 0.7 ≲z≲ 0.86. We identify 10,470 galaxies withzexcesses in the COSMOS data set and 91,385 in the NEP field. We cross-reference the COSMOS EELG sample with the zCOSMOS and DEIMOS 10k spectral catalogs, finding 1395 spectroscopic matches. We made an additional 71 (46 unique) spectroscopic measurements withY< 23 using the HYDRA multiobject spectrograph on the WIYN 3.5 m telescope, and 204 spectroscopic measurements from the DEIMOS spectrograph on the Keck II telescope, providing a total of 1441/10,470 spectroscopic redshifts for the EELG sample in COSMOS (∼14%). We confirm that 1418 (∼98%) are Hαor [Oiii]λ5007 emitters in the above stated redshift ranges. We also identify 240 redshifted Hαand [Oiii]λ5007 emitters in the NEP using spectra taken with WIYN/HYDRA and Keck/DEIMOS. Using broadband-selection techniques in theg−r−icolor space, we distinguish between Hαand [Oiii]λ5007 emitters with 98.6% accuracy. We test our EELG selection by constructing Hαand [Oiii]λ5007 luminosity functions and comparing to recent literature results. We conclude that broadband magnitudes from HSC, the Vera C. Rubin Observatory, and other deep optical multiband surveys can be used to select EELGs in a straightforward manner.