Ultracool Dwarf Absolute Magnitude Versus Spectral Type Relations for Euclid and Roman Near-infrared Filters

We synthesize Euclid Near Infrared Spectrometer and Photometer photometry for the Y _E J _E H _E filters and Roman Wide Field Instrument photometry for the F106, F129, F146, F158, F184 and F213 filters using SpeX prism spectra and parallaxes of 688 field-age and 151 young (≲200 Myr) ultracool dwarfs (spectral types M6–T9). For the above filters, we derive empirical absolute magnitude-spectral type polynomial relations that enable the calculation of photometric distances for ultracool dwarfs to be observed with Euclid and Roman, in the absence of parallax measurements. The synthesized photometry can also be used to generate color–color figures to distinguish high-redshift galaxies from brown dwarf interlopers.