A large, deep 3 deg2 survey of H α, [O iii], and [O ii] emitters from LAGER: constraining luminosity functions

Abstract

We present our measurements of the Hα, [Oiii], and [Oii] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 z = 0.47 Hα-, 3933 z = 0.93 [Oiii]-, and 5367 z = 1.59 [Oii]selected emission line galaxies in a 3 deg 2 single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10 −18 erg s −1 cm −2 and comoving volumes of (1 − 7) × 10 5 Mpc 3 making our survey one of the deepest narrowband surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and color-color selections. We measure the observed luminosity functions for each sample and find best-fits of φ = 10 −3.16 +0.09 −0.09 Mpc −3 and L = 10 41.72 +0.09 −0.09 erg s −1 for Hα, φ = 10 −2.16 +0.10 −0.12 Mpc −3 and L = 10 41.38 +0.07 −0.06 erg s −1 for [Oiii], and φ = 10 −1.97 +0.07 −0.07 Mpc −3 and L = 10 41.66 +0.03 −0.03 erg s −1 for [Oii], with α fixed to −1.75, −1.6, and −1.3, respectively. An excess of bright > 10 42 erg s −1 [Oiii] emitters is observed and may be due to AGN contamination. Corrections for dust attenuation are applied assuming A Hα = 1 mag. We also design our own empirical rest-frame g − r calibration using SDSS DR12 data, test it against our z = 0.47 Hα emitters with zCOSMOS 1D spectra, and calibrate it for (g − r) between −0.8 and 1.3 mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as log 10 ρ SFR /(M yr −1 Mpc −3 ) = −1.63 ± 0.04, −1.07 ± 0.06, and −0.90 ± 0.10 for Hα, [Oiii], and [Oii], respectively. We find our [Oiii] and [Oii] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multi-wavelength SFRDs, while the Hα sample traces ∼ 70 percent of the total z = 0.47 SFRD.

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

“…Hereafter, when referring to HAEs or O3Es, we also imply that each species lies in these redshift bounds, and that [OIII] refers to [OIII]λ5007 unless otherwise stated. Our 94% overall sample purity is very comparable to the purities seen in narrowband surveys at similar redshifts, e.g., 95% for Hα at z = 0.84 (Sobral et al 2013), 93.7% for Hα at z = 0.47, and 90.4% for [OIII] at z = 0.93 (Khostovan et al 2020). We summarize our spectroscopically confirmed HAEs and O3Es in Table 1.…”

“…We construct our [OIII] LFs in much the same way as the Hα LFs, except that we do not include an AGN contamination correction. This allows us to make a more direct comparison with other studies that also lack an AGN correction, such as Khostovan et al (2020). In contrast to the Hα LFs, our COSMOS and HEROES ) ∼ 41.75 erg s −1 .…”

“…While we considered performing a dust attenuation correction of our own data, we found that our spectroscopic datasets were insufficiently calibrated to provide reliable Hα/Hβ line ratios for calibrating dust attenuation with the Balmer decrement. Khostovan et al (2020) noted the same difficulty with the zCOSMOS dataset and instead opted for a dust correction based on g − r colors. We refrained from using such a correction to avoid any potential bias introduced by using g − r color for both dust attenuation and differentiation between HAEs and O3Es.…”

The OTELO survey

“…On the other hand, our result seems to agreed with the trend observed in other works and cited in Hayashi et al (2013), where the authors found that [O ii]3727 emitters selected by narrow-band (NB) techniques are likely to be dust-poor systems. For example, both Hayashi et al (2013) and Khostovan et al (2020) give A Hα ∼ 0.35 mag for emitters at z ∼ 1.47, Hayashi et al (2015) found A Hα = 0.63 mag for z = 1.5, and Khostovan et al (2015) obtains A Hα = 0.55 ± 0.12 mag for emitters at z = 1.59. Nevertheless, the large dispersion of the mean value derived makes difficult to obtain a clear conclusion about the absorption nature of our emitters.…”

“…Other works have used the combination of Hβ and [O iii], for example De Barros et al (2019) reaching as far as z ∼ 8; Khostovan et al (2015) up to 0.84 < z < 3.24; and Sobral et al (2015) up to z = 1.4. In addition, there are a series of works were the LF is obtained by employing the doublet [O iii] λλ4959,5007 alone, for example, in Ly et al (2007) at 0.41 < z < 0.84; Bongiovanni et al (2020) at z ∼ 0.83; Khostovan et al (2020) at 0.91 < z < 1.10; or Hayashi et al (2020) at 0.05 < z < 0.94.…”