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The NIRCam-NIRSpec GTO galaxy assembly survey

The NIRCam-NIRSpec GTO galaxy assembly survey is an ambitious imaging and spectroscopic deep-field survey to study the formation and evolution of galaxies from z ≥ 12 to z ∼ 2. It will put together NIRSpec, NIRCam, and MIRI data, alongside the deepest data from HST, Chandra, ALMA, and JVLA, to produce an unprecedented view of high-redshift galaxies. This survey is a collaboration of the NIRSpec and NIRCam GTO teams, and it combines imaging and spectroscopy as well as full use of coordinated parallel observations to get the best out of all three instruments.

We will conduct a two-tier, ‘Deep’ and ‘Medium’, survey. Each includes at least 9 bands of NIRCam imaging as well as spectroscopy from 0.7–5.2μm at resolutions R = 100–2700. This is complemented by deep MIRI parallel pointings at 7.7 and 12.8 μm.

The 'Deep' survey will cover 46 arcmin2, centered on the HUDF/GOODS-S, with NIRCam imaging to a limit of AB=29.8 (10-σ point source) and a peak exposure time of 120 ksec in F115W. We will conduct two NIRSpec pointings with total integration of 200 ksec each, with an emphasis on z>6 galaxies; the first will be centered on the HUDF and will use pre-flight targets, the second will be based on the NIRCam imaging.

The 'Medium' survey will cover another 190 arcmin2, in both GOODS-S and GOODS-N, with NIRCam imaging to a limit of AB=28.8 (10-σ point source) and with MIRI imaging of 14 arcmin2, reaching AB=26.7 in F770W in 8 arcmin2. We will conduct 12 NIRSpec pointings (43 ksec each, total over the gratings) targeted from JWST imaging, and 12 NIRSpec pointings (13 ksec each) targeted from pre-flight imaging, notably CANDELS. These will provide over 5000 spectra of faint galaxies, including many on the deeper imaging.

The overall survey will provide the rest-frame optical data of sufficient area, depth, and spectral resolutions to map galaxy population properties, including the joint distribution of stellar mass, luminosity, star formation rate, stellar ages, sizes, metallicity, nuclear activity, gas kinematics, and outflows, over a wide range of redshifts. Broadly speaking, spectroscopy (at R = 100, 1000, and 2700) provides precise and robust redshifts, measurement of the stellar continuum, and emission lines to z ∼ 10 and beyond. The emission lines allow us to diagnose the galaxies’ star formation rate (SFR), metallicities, chemical abundances, the ISM dust-reddening, and the ISM excitation, including signatures of AGNs. Low-resolution spectroscopy (R=100) for the brighter objects can also diagnose the stellar populations (especially the stellar age distribution). High-resolution spectroscopy (R=2700) can diagnose internal galaxy kinematics and outflows.

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