The 7-Dimensional Sky Survey
Wide-area, high-cadence and deep, on one tile grid and one instrument. 7DS trades area against depth across three tiers that share a single observational infrastructure.
Three tiers, one grid
7DS is the science program of 7DT. It is structured as three complementary surveys distinguished by area, cadence and depth: the Reference Imaging Survey (RIS), the Wide-area Time-domain Survey (WTS), and the Intensive Monitoring Survey (IMS). Across the three tiers sky coverage decreases and depth increases, spanning the range from a single-visit all-southern-sky reference map to daily monitoring of a small field, while sharing a single observational infrastructure.
| Property | RIS | WTS | IMS |
|---|---|---|---|
| Survey area | 23,000 deg² | 800–1,200 deg² | 8.5 deg² |
| Target region | Dec < +20° | Fields with near-infrared ancillary data | AKARI / SPHEREx Deep Field South |
| Cadence | Single visit | 10–14 days | 1 day |
| Depth | 19.1 mag | 22.2 mag* | 23.6 mag* |
| Status | Observing | Commencing 2026 | Observing |
Depths are 5σ point-source limits in the m600 band. The RIS figure is a single-visit depth (3 × 100 s); the WTS and IMS figures are expected values from cumulative data after five years of operation.
What each survey is for
Reference Imaging Survey
ObservingThe wide-area component of 7DS. Every tile of the southern sky is observed once with the full set of available medium bands, in three consecutive 100-second exposures. RIS images serve two purposes at once: reference frames against which transients are identified by difference imaging, and a homogeneous spectrophotometric map of the southern sky usable for galaxy population studies, photometric redshift catalogs and quasar identification. Full-cycle completion is anticipated by the end of 2027.
5σ depths range from 19.7 mag at m400 to 17.2 mag at m875.
Wide-area Time-domain Survey
Commencing 2026WTS extends 7DS into the time domain over a moderately wide area, sustained over a five-year operational period. Field selection prioritizes regions with existing near-infrared coverage, including the VISTA Kilo-degree Infrared Galaxy (VIKING) survey footprint and the Vera C. Rubin Observatory Deep Drilling Fields, so that 7DT data are complemented at wavelengths the array cannot reach. Roughly 90 to 100 visits per tile accumulate to 22.0–22.5 mag in the majority of medium bands.
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.
Intensive Monitoring Survey
ObservingThe deep, high-cadence component of 7DS. Seven tiles near the south ecliptic pole are observed every available night with the full medium-band set. The field was deliberately chosen to overlap the SPHEREx Deep Field South, so that 7DT optical medium-band photometry is co-located with SPHEREx near-infrared spectrophotometry within the same survey volume — a choice that maximizes the synergy between the two surveys for photometric redshifts and for spatially resolved studies of faint sources.
Field center: RA 05h13m07.36s, Dec −60°28′11.71″. Observing time budget of 20,000 minutes per year.