The Blue Jay survey: Deep JWST spectroscopy for a representative sample of galaxies at cosmic noon

We present the Blue Jay survey, a cycle 1 JWST program aimed at studying the stellar and gas content of galaxies at cosmic noon. The survey consists of deep spectroscopy for 153 targets observed over two pointings in the COSMOS field using the NIRSpec micro-shutter assembly (MSA). We employed the three medium-resolution gratings, G140M, G235M, and G395M, with exposure times of 13 hours, 3.2 hours, and 1.6 hours, respectively. We thus obtained full coverage of the 1 - 5 m range, corresponding to the entire rest-frame optical wavelength range, with a spectral resolution R M_⊙ to 10^ Parallel observations provided deep multiband NIRCam imaging, which partially overlaps with the spectroscopic observations. The sample was carefully selected to provide a census of galaxies over the redshift range 1.7 < z < 3.5 above a redshift-dependent minimum stellar mass that ranges from 10^ 8.7 9.3 M_⊙. The selection ensured 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 constructed a master background from empty shutters and subtracted it from each of the science spectra. This in turn allowed us to use 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. In order to obtain self-consistent fits of spectroscopic and photometric data, we measured multiband photometry using space-based observations from the exact area in the sky where the NIRSpec 1D spectrum is extracted. The spectra contain a wealth of emission and absorption lines, including hydrogen lines (Balmer and Paschen series), helium lines, metal emission lines from ionized gas, metal stellar absorption lines, and resonant absorption lines that can be used to study neutral gas (Na I D and Ca II H, K). Spectroscopic redshifts are unambiguously measured for 93% of the sample. 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.