The Blue Jay JWST galaxy sample properties

The selection ensures that the Blue Jay sample is representative of the entire galaxy population at these redshifts, without strong biases in color, star formation rate, or other properties. The sizes of massive galaxies at these redshifts are comparable to, or larger than the NIRSpec shutters, which requires custom strategies for designing and reducing the observations. Since the standard A-B nod subtraction leads to flux self-subtraction for large galaxies, we construct a master background from empty shutters and subtract it from each of the science spectra.

This, in turn, allows for the use of shorter slitlets consisting of only two shutters per galaxy instead of the usual three, with a substantial increase in the multiplexing of the NIRSpec MSA. Another problem introduced by the small shutter size is the mismatch between the galaxy region probed by NIRSpec and that probed by photometric measurements. For this reason, we measure multi-band photometry using archival JWST and Hubble Space Telescope observations in two different ways: source photometry is measured in a large elliptical aperture encompassing the entire source, while box photometry is measured from the exact area in the sky where the NIRSpec 1D spectrum is extracted.

This enables self-consistent fits of spectroscopic and photometric data. The Blue Jay dataset, which we publicly release, represents the ideal sample for studying the stellar populations, neutral gas, and ionized gas in Cosmic Noon galaxies, including star formation histories, quenching, outflows, metallicity, and dust attenuation.