[Paper Review] JEMS: A deep medium-band imaging survey in the Hubble Ultra-Deep Field with JWST NIRCam & NIRISS

Christina C. Williams, Sandro Tacchella+33 more|arXiv (Cornell University)|Jan 24, 2023

Radio Astronomy Observations and Technology12 citations

TL;DR

JEMS is the first public JWST medium-band imaging survey using multiple 2–5 μm filters (NIRCam and NIRISS) in the HUDF, enabling spatially resolved emission-line and continuum studies up to z~20 and providing a data release of science-ready mosaics.

ABSTRACT

We present JEMS (JWST Extragalactic Medium-band Survey), the first public medium-band imaging survey carried out using JWST/NIRCam and NIRISS. These observations use $\sim2μ$m and $\sim4μ$m medium-band filters (NIRCam F182M, F210M, F430M, F460M, F480M; and NIRISS F430M & F480M in parallel) over 15.6 square arcminutes in the Hubble Ultra Deep Field (UDF), thereby building on the deepest multi-wavelength public datasets available anywhere on the sky. We describe our science goals, survey design, NIRCam and NIRISS image reduction methods, and describe our first data release of the science-ready mosaics. Our chosen filters create a JWST imaging survey in the UDF that enables novel analysis of a range of spectral features potentially across the redshift range of $0.31$ magnitude) across redshifts $1.5

Motivation & Objective

• Motivate and design a medium-band imaging survey with JWST to sample SED features and emission lines across a broad redshift range (0.3 < z < 20).
• Leverage five medium-band filters to break degeneracies in galaxy properties and improve photometric redshifts and line flux estimates.
• Provide deep, high-resolution, spatially resolved information on emission lines (e.g., Hα, Paα, [O III]+Hβ) in the HUDF and enable robust comparisons with ancillary data.

Proposed method

• Use five JWST/NIRCam medium-band filters (F182M, F210M, F430M, F460M, F480M) and parallel NIRISS F430M & F480M to cover ~15.6 arcmin^2 in HUDF.
• Deep integrations (2 μm and 4 μm bands) totaling ~15.5 hours science exposure time across filters; include coordinated NIRISS parallel to extend 4 μm coverage by ~50%.
• Process JWST data with standard pipeline (Stage 1–3) plus custom corrections for 1/f noise, wisps, background modeling, and astrometric alignment to Gaia-backed HST catalogs.
• Perform source detection on stacked and per-filter mosaics; execute forced photometry in 0.3” apertures and estimate uncertainties via random apertures to include pixel covariance.
• Provide science-ready mosaics and document reduction, calibration context, and data products for public use.

Experimental results

Research questions

• RQ1 How well can JWST medium-band imaging sample key spectral features across 0.3 < z < 20?
• RQ2 Can medium-band colors efficiently identify strong emission-line galaxies and constrain line fluxes at high redshift?
• RQ3 What are the depths, source counts, and photometric performance of a JWST medium-band survey in HUDF?
• RQ4 How can medium-band photometry complement broad-band JWST surveys and spectroscopic programs in the same field?

Key findings

• Detected 10,686 objects in the stacked NIRCam imaging; 4,876–4,876 sources per individual filter (F182M, F210M, F430M, F460M, F480M).
• NIRISS detected 2,767 objects in F430M and 1,976 in F480M within the parallel footprint.
• 5σ point-source depths (0.3” aperture, aperture-corrected) reach 29.3 mag (F182M), 29.2 mag (F210M), 28.5 mag (F430M), 28.3 mag (F460M), and 28.6 mag (F480M) for NIRCam; 28.4 mag (F430M) and 28.2 mag (F480M) for NIRISS.
• The medium-band colors efficiently trace strong line emitters at 1.5 < z < 9.3, notably Hα+[N II] and [O III]+Hβ, enabling emission-line based inferences across cosmic time.
• First data release provides science-ready mosaics for community use and demonstrates the potential of JWST medium-band imaging to complement spectroscopic surveys and inform future survey strategies.