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

TL;DR

The Blue Jay survey delivers deep rest-frame optical spectroscopy for a representative sample of Cosmic Noon galaxies using JWST/NIRSpec MOS across $1-5\,\mu$m, enabling simultaneous study of stellar populations, neutral gas, and ionized gas. The program uses three medium-resolution gratings to achieve $R\sim1000$ over $1.7<z<3.5$, with two pointings in COSMOS and a master background subtraction to maximize multiplexing for large galaxies. A key methodological advance is matched spectro-photometric analysis, wherein photometry is extracted in a box aperture that matches the NIRSpec slit footprint, paired with 1D spectra from the same region to enable self-consistent fits. The data products, including 2D/1D spectra, box and elliptical photometry, and MSA configurations, are publicly released, enabling broad studies of stellar populations, ISM, dust, and quenching mechanisms in Cosmic Noon galaxies, with several early results highlighting neutral outflows and AGN-related feedback as drivers of rapid quenching.

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.

Figures (19)

• Figure 1: Assessing the completeness of the CANDELS/COSMOS catalog. Top: source count for the CANDELS/COSMOS and the HUDF catalogs, as a function of the F160W magnitude. The HUDF source counts have been normalized to account for the smaller area. Bottom: we estimate the completeness of the catalog by taking the ratio of the source counts shown in the top panel. The blue line represents a B-spline fit. The vertical dashed lines mark the 90% and 50% completeness limits.
• Figure 2: Discrepancy in photometric redshift (top) and stellar mass (bottom) between the values in the 3D-HST catalog and those from the Prospector emulator, as a function of magnitude, for all galaxies in the parent catalog with redshift in the range $1.7 < z < 3.5$. The stellar mass discrepancy is -0.16 dex (median value, shown by the dashed purple line).
• Figure 3: Distribution of stellar masses and photometric redshifts for the parent sample. The redshift range of the Blue Jay survey, $1.7 < z < 3.5$ is shown in red, while the mass completeness limit is shown in blue. In the region defined by these boundaries, galaxies are color-coded by the spectroscopic weight assigned to them.
• Figure 4: Footprints of the NIRSpec shutters for galaxy 10592 ($z=1.8$, $\log M_\star/M_\odot=11.2$), illustrating the 2-point nodding adopted by Blue Jay. Given the large size of the galaxy, it is not possible to derive a local background from shutters adjacent to the primary shutter -- instead, a master background must be used. The galaxy image is from NIRCam F200W.
• Figure 5: Blue Jay NIRSpec pointings (in orange; each pointing consists of four MSA quadrants) and parallel NIRCam fields (in blue; each field consists of two separate arrays of $2\times2$ detectors). The NIRCam North field was observed in parallel to the NIRSpec North pointing. The background image is the HST F160W mosaic of the CANDELS/COSMOS field.