The Blue Jay Survey: Deep JWST Spectroscopy for a Representative Sample of Galaxies at Cosmic Noon

Sirio Belli; Letizia Bugiani; Minjung Park; J. Trevor Mendel; Rebecca L. Davies; Amir H. Khoram; Benjamin D. Johnson; Joel Leja; Sandro Tacchella; Vanessa Brown; Charlie Conroy; Razieh Emami; Yijia Li; Caterina Liboni; Gabriel Maheson; Elijah P. Mathews; Rohan P. Naidu; Erica J. Nelson; Bryan A. Terrazas; Rainer Weinberger

arXiv · 2510.11775

The Blue Jay Survey: Deep JWST Spectroscopy for a Representative Sample of Galaxies at Cosmic Noon

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Abstract

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 employ 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 obtain full coverage of the 1-5 micron range, corresponding to the entire rest-frame optical wavelength range. The sample is 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 Msun to 10^9.3 Msun.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 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, 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. We measure multi-band photometry using archival JWST and HST observations in two different ways: in a large elliptical aperture encompassing the entire source and 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.

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Sirio Belli, Letizia Bugiani, Minjung Park, J. Trevor Mendel, Rebecca L. Davies, Amir H. Khoram, Benjamin D. Johnson, Joel Leja, Sandro Tacchella, Vanessa Brown, Charlie Conroy, Razieh Emami, Yijia Li, Caterina Liboni, Gabriel Maheson, Elijah P. Mathews, Rohan P. Naidu, Erica J. Nelson, Bryan A. Terrazas, Rainer Weinberger. 2025-10-13. The Blue Jay Survey: Deep JWST Spectroscopy for a Representative Sample of Galaxies at Cosmic Noon. https://arxiv.org/abs/2510.11775

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