The james webb space telescope north ecliptic pole time-domain field. I. Field selection of a JWST community field for time-domain studies

We describe the selection of the James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-domain Field (TDF), a ≳14′ diameter field located within JWST’s northern continuous viewing zone (CVZ) and centered at (R.A., decl.)_J2000=(17:22:47.896, +65:49:21.54). We demonstrate that this is the only region in the sky where JWST can observe a clean (i.e., free of bright foreground stars and with low Galactic foreground extinction) extragalactic deep survey field of this size at arbitrary cadence or at arbitrary orientation, and without a penalty in terms of a raised zodiacal background. This will crucially enable a wide range of new and exciting time-domain science, including high-redshift transient searches and monitoring (e.g., SNe), variability studies from active galactic nuclei (AGNs) to brown dwarf atmospheres, as well as proper motions of possibly extreme scattered Kuiper Belt and Inner Oort Cloud Objects, and of nearby Galactic brown dwarfs, low-mass stars, and ultracool white dwarfs. A JWST/NIRCam+NIRISS GTO program will provide an initial 0.8–5.0 μm spectrophotometric characterization to m_AB ∼ 28.8±0.3 mag of four orthogonal “spokes” within this field. The multi-wavelength (radio through X-ray) context of the field is in hand (ground-based near–UV-visible–near-IR), in progress (VLA 3 GHz, VLBA 5 GHz, HST UV-visible, Chandra X-ray, and IRAM 30 m 1.3 and 2 mm), or scheduled (JCMT 850 μm). We welcome and encourage ground-and space-based follow-up of the initial GTO observations and ancillary data, to realize its potential as an ideal JWST time-domain community field.