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      The GREATS H\(\beta\)+[OIII] Luminosity Function and Galaxy Properties at \(\mathbf{z\sim8}\): Walking the Way of JWST


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          The James Webb Space Telescope will allow to spectroscopically study an unprecedented number of galaxies deep into the reionization era, notably by detecting [OIII] and H\(\beta\) nebular emission lines. To efficiently prepare such observations, we photometrically select a large sample of galaxies at \(z\sim8\) and study their rest-frame optical emission lines. Combining data from the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and from HST, we perform spectral energy distribution (SED) fitting, using synthetic SEDs from a large grid of photoionization models. The deep Spitzer/IRAC data combined with our models exploring a large parameter space enables to constrain the [OIII]+H\(\beta\) fluxes and equivalent widths for our sample, as well as the average physical properties of \(z\sim8\) galaxies, such as the ionizing photon production efficiency with \(\log(\xi_\mathrm{ion}/\mathrm{erg}^{-1}\hspace{1mm}\mathrm{Hz})\geq25.77\). We find a relatively tight correlation between the [OIII]+H\(\beta\) and UV luminosity, which we use to derive for the first time the [OIII]+H\(\beta\) luminosity function (LF) at \(z\sim8\). The \(z\sim8\) [OIII]+H\(\beta\) LF is higher at all luminosities compared to lower redshift, as opposed to the UV LF, due to an increase of the [OIII]+H\(\beta\) luminosity at a given UV luminosity from \(z\sim3\) to \(z\sim8\). Finally, using the [OIII]+H\(\beta\) LF, we make predictions for JWST/NIRSpec number counts of \(z\sim8\) galaxies. We find that the current wide-area extragalactic legacy fields are too shallow to use JWST at maximal efficiency for \(z\sim8\) spectroscopy even at 1hr depth and JWST pre-imaging to \(\gtrsim30\) mag will be required.

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          Overview of the near-infrared spectrograph (NIRSpec) instrument on-board the James Webb Space Telescope (JWST)


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            22 March 2019


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            13 pages, 9 figures, accepted for publication in MNRAS

            Galaxy astrophysics


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