Subaru/HSC z-Broadband Excess Selection of Extreme Emission Line Galaxies at z<1

Abstract

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 broadband, which is sensitive to Hα at 0.3 z 0.42 and [OIII]λ5007 at 0.7 z 0.86. We identify 10,470 galaxies with z excesses in the COSMOS dataset 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 multi-object spectrograph on the WIYN 3.5m 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 [OIII]λ5007 emitters in the above stated redshift ranges. We also identify 240 redshifted Hα and [OIII]λ5007 emitters in the NEP using spectra taken with WIYN/HYDRA and Keck/DEIMOS. Using broadband selection techniques in g − r − i color space, we distinguish between Hα and [OIII]λ5007 emitters with 98.6% accuracy. We test our EELG selection by constructing Hα and [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 multi-band surveys can be used to select EELGs in a straightforward manner.