What is the JWST NEP TDF?

The James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF), or WTDF for short, is a 14′ diameter region of the sky selected to be ideal for ultra-deep (m_AB ~ 29 mag) time-domain science with JWST (Jansen & Windhorst 2018), that is being developed as a community field. Located within JWST's northern Continuous Viewing Zone, it can be observed at any cadence or orientation, is devoid of stars bright enough to deeply saturate JWST's sensitive NIRCam detectors, has low Galactic foreground extinction, and will be targeted by GTO program 2738 (PI: R. Windhorst) with NIRCam and NIRISS. It is the only region in the sky where JWST can observe a clean extragalactic deep survey field of this size at arbitrary cadence and orientation, enabling a wide range of new and exciting time-domain science, including high redshift transient searches and monitoring (e.g., supernovae), variability studies from Active Galactic Nuclei (AGN) to brown dwarf atmospheres, as well as proper motions of extreme scattered Kuiper Belt Objects and comets beyond the distance of Neptune, and of nearby Galactic brown dwarfs, low-mass stars, and ultracool white dwarfs. In anticipation of JWST's launch, on December 25 2021, a wealth of ancillary data across the electromagnetic spectrum (X-ray–radio) had already been collected. This includes deep (~0.9 μJy rms) VLA 3GHz radio observations and Large Binocular Telescope and Subaru Ugriz (m_AB ~ 26.5 mag) and MMT/MMIRS YJHKs (m_AB ~ 24.5–22 mag) photometry of the entire JWST NEP TDF, as well as Hubble Space Telescope WFC3+ACS UV–Visible observations of the central r < ~7.5′.