2022ApJ...928...78R

We present a search for extreme emission line galaxies (EELGs) at z < 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 the z broad band, which is sensitive to Hα at 0.3 <= z <= 0.42 and [O III]λ5007 at 0.7 <= z <= 0.86. We identify 10,470 galaxies with zexcesses 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 with Y < 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 Hα or [O III]λ5007 emitters in the above stated redshift ranges. We also identify 240 redshifted Hα and [O III]λ5007 emitters in the NEP using spectra taken with WIYN/HYDRA and Keck/DEIMOS. Using broadband-selection techniques in the g - r - i color space, we distinguish between Hα and [O III]λ5007 emitters with 98.6% accuracy. We test our EELG selection by constructing Hα and [O III]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.