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Mapping out the populations of thick disk and halo brown dwarfs is importantfor understanding the metallicity dependence of low-temperature atmospheres andthe substellar mass function. Recently, a new population of cold and metal-poorbrown dwarfs has been discovered, with $T_{\rm{eff}}$ $\lesssim$ 1400 K andmetallicity $\lesssim$ $-$1 dex. This population includes what may be the firstknown "extreme T-type subdwarfs" and possibly the first Y-type subdwarf, WISEAJ153429.75$-$104303.3. We have conducted a Gemini YJHK/Ks photometric follow-upcampaign targeting potentially metal-poor T and Y dwarfs, utilizing the GNIRSand Flamingos-2 instruments. We present 14 near-infrared photometric detectionsof 8 unique targets: six T subdwarf candidates, one moderately metal poor Ydwarf candidate, and one Y subdwarf candidate. We have obtained the first everground-based detection of the highly anomalous object WISEAJ153429.75$-$104303.3. The F110W$-$$J$ color of WISEA J153429.75$-$104303.3 issignificantly bluer than that of other late-T and Y dwarfs, indicating thatWISEA J153429.75$-$104303.3 has an unusual spectrum in the 0.9-1.4 $\mu$mwavelength range which encompasses the $J$-band peak. Our $J$-band detection ofWISEA J153429.75$-$104303.3 and corresponding model comparisons suggest asubsolar metallicity and temperature of 400-550 K for this object. JWSTspectroscopic follow-up at near-infrared and mid-infrared wavelengths wouldallow us to better understand the spectral peculiarities of WISEAJ153429.75$-$104303.3, assess its physical properties, and conclusivelydetermine whether or not it is the first Y-type subdwarf.

Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs