Wide-area Time-domain Survey
A moderately wide area revisited every 10 to 14 days for five years, in fields where near-infrared data already exist.
What this survey is for
Follow what changes on timescales of weeks, and stack deep enough to reach faint galaxies.
A single epoch measures what is present, not what is changing. WTS covers a smaller area in order to revisit it every 10 to 14 days, an interval matched to what evolves on that timescale: reverberation in active galactic nuclei, long-period variable and eclipsing stars, and slow extragalactic transients such as superluminous supernovae and tidal disruption events. Repetition also accumulates depth: 90 to 100 visits per tile stack to 22.0–22.5 mag across most medium bands, sufficient for photometric redshifts on galaxies well below the single-visit limit. Fields are selected where near-infrared data already exist — the VIKING footprint and the Rubin Deep Drilling Fields — covering wavelengths 7DT cannot reach.
Cadence over area
| Area | 800–1,200 deg² |
|---|---|
| Field selection | Fields with near-infrared ancillary data |
| Cadence | 10–14 days |
| Visits per tile | 90–100 over five years |
| Cumulative depth | 22.0–22.5 mag in most medium bands |
| Status | Commencing 2026 |
Not yet started
WTS is scheduled to commence in 2026. Fields are being selected to overlap existing near-infrared coverage — the VISTA Kilo-degree Infrared Galaxy survey footprint and the Vera C. Rubin Observatory Deep Drilling Fields are the leading candidates — so that 7DT medium-band photometry is complemented at wavelengths the array cannot reach. Until observations begin there is no coverage to report; tiles observed under the Reference Imaging Survey in these fields already exist and are shown on the data access page.
What the cadence is chosen for
Science cases include reverberation mapping of AGN, long-period variables and eclipsing systems, and slow-evolving extragalactic transients such as superluminous supernovae and tidal disruption events.
Stacking 90 to 100 visits also reaches 22.0–22.5 mag across most of the medium bands, deep enough for photometric redshifts on galaxies well below the single-visit limit. Forecast redshift precision for the stacked survey is given under cosmology and photometric redshifts.