unTimely: a Full-sky, Time-domain unWISE Catalog

We present the unTimely Catalog, a deep time-domain catalog of detections based on Wide-field Infrared Survey Explorer (WISE) and NEOWISE observations spanning the 2010 through 2020 time period. Detections are extracted from “time-resolved unWISE coadds,” which stack together each biannual sky pass of WISE imaging to create a set of ∼16 all-sky maps (per band), each much deeper and cleaner than individual WISE exposures. unTimely incorporates the W1 (3.4 μ m) and W2 (4.6 μ m) channels, meaning that our data set effectively consists of ∼32 full-sky unWISE catalogs. We run the crowdsource crowded-field point-source photometry pipeline (Schlafly et al. 2018) on each epochal coadd independently, with low detection thresholds: S/N = 4.0 (2.5) in W1 (W2). In total, we tabulate and publicly release 23.5 billion (19.9 billion) detections at W1 (W2). unTimely is ∼1.3 mag deeper than the WISE/NEOWISE Single Exposure Source Tables near the ecliptic, with further enhanced depth toward higher ecliptic latitudes. The unTimely Catalog is primarily designed to enable novel searches for faint, fast-moving objects, such as Y dwarfs and/or late-type (T/Y) subdwarfs in the Milky Way’s thick disk or halo. unTimely will also facilitate other time-domain science applications, such as all-sky studies of quasar variability at mid-infrared wavelengths over a decade-long time baseline.