Thirteen New M Dwarf + T Dwarf Pairs Identified with WISE/NEOWISE

We present the discovery of 13 new widely separated T dwarf companions to M dwarf primaries, identified using WISE/NEOWISE data by the CatWISE and Backyard Worlds: Planet 9 projects. This sample represents a ∼60% increase in the number of known M+T systems, and allows us to probe the most extreme products of binary/planetary system formation, a discovery space made available by the CatWISE2020 catalog and the Backyard Worlds: Planet 9 effort. Highlights among the sample are WISEP J075108.79-763449.6, a previously known T9 thought to be old due to its SED, which we now find is part of a common-proper-motion pair with L 34-26 A, a well studied young M3 V star within 10 pc of the Sun; CWISE J054129.32–745021.5 B and CWISE J055816.34–450155.0 B, two T8 dwarfs possibly associated with the very fast-rotating M4 V stars CWISE J054129.32–745021.5 A and CWISE J055816.34–450155.0 A; and UCAC3 40-6918 B, which is among the widest late T companions to main sequence stars, with a projected separation of ∼7100 au. The new benchmarks presented here are prime JWST targets, and can help us place strong constraints on formation and evolution theory of substellar objects as well as on atmospheric models for these cold exoplanet analogs.