# Deep Full-sky Coadds from Three Years of WISE and NEOWISE Observations

## TL;DR

This paper presents the creation of the deepest full-sky maps at 3-5 microns from three years of WISE/NEOWISE data, enabling improved deep photometry for astronomical surveys and target selection.

## Contribution

It introduces a novel reprocessing pipeline that combines all available WISE/NEOWISE exposures to produce high-resolution, deep full-sky coadds with artifact removal for enhanced astronomical analysis.

## Key findings

- Coadds are ~3 times deeper than previous AllWISE stacks.
- Forced photometry depths are increased by 0.56 and 0.46 magnitudes in W1 and W2.
- The new maps facilitate uniform target selection and searches for rare objects.

## Abstract

We have reprocessed over 100 terabytes of single-exposure WISE/NEOWISE images to create the deepest ever full-sky maps at 3-5 microns. We incorporate all publicly available W1 and W2 imaging - a total of ~8 million exposures in each band - from ~37 months of observations spanning 2010 January to 2015 December. Our coadds preserve the native WISE resolution and feature depth of coverage ~3 times greater than that of the AllWISE Atlas stacks. Our coadds are designed to enable deep forced photometry, in particular for the Dark Energy Camera Legacy Survey (DECaLS) and Mayall z-Band Legacy Survey (MzLS), both of which are being used to select targets for the Dark Energy Spectroscopic Instrument (DESI). We describe newly introduced processing steps aimed at leveraging added redundancy to remove artifacts, with the intent of facilitating uniform target selection and searches for rare/exotic objects (e.g. high-redshift quasars and distant galaxy clusters). Forced photometry depths achieved with these coadds extend 0.56 (0.46) magnitudes deeper in W1 (W2) than is possible with only pre-hibernation WISE imaging.