unWISE Coadds: The Five-year Data Set

TL;DR

This paper introduces five-year, full-sky coadded infrared maps from WISE/NEOWISE data, significantly deeper than previous releases, enabling detection of fainter sources and long-term variability studies.

Contribution

The paper presents the deepest all-sky infrared maps at 3-5 microns, combining five years of data with improved processing for astrometry and artifact removal, and introduces time-resolved coadds for motion analysis.

Findings

Deep five-year coadds are twice as sensitive as AllWISE.

New time-resolved coadds enable variability and motion measurements.

Processed maps are used for target selection in DESI and future missions.

Abstract

We present full-sky coadded maps created by uniformly combining the first five years of Wide-field Infrared Survey Explorer (WISE) and NEOWISE imaging at 3.4 microns (W1) and 4.6 microns (W2). By incorporating both pre-hibernation WISE exposures from 2010-2011 and the first four years (2013-2017) of post-hibernation exposures from the NEOWISE-Reactivation mission, we are able to provide W1/W2 coadds that span a 15 times longer time baseline and are substantially deeper than the standard AllWISE data products. Our new five-year "full-depth" coadds are now the deepest ever all-sky maps at 3-5 microns, permitting detection of sources ~2 times (~0.7 mag) fainter than AllWISE at 5 sigma significance. We additionally present an updated set of "time-resolved" W1/W2 coadds, which separately stack each of ~10 sky passes at each inertial sky location, enabling motion and variability measurements for faint infrared sources over a long ~7.5 year time baseline. We highlight new processing improvements relative to our previous "unWISE" coadd releases, focusing on astrometric calibration and artifact flagging. The deep WISE stacks presented here are already being used to perform target selection for the Dark Energy Spectroscopic Instrument (DESI), and our full-sky coadded WISE/NEOWISE products will be key precursor data sets for upcoming wide-field infrared missions including SPHEREx and NEOCam.