  Y dwarfs provide a unique opportunity to study free-floating objects with
masses $<$30 M$_{Jup}$ and atmospheric temperatures approaching those of known
Jupiter-like exoplanets. Obtaining distances to these objects is an essential
step towards characterizing their absolute physical properties. Using
Spitzer/IRAC [4.5] images taken over baselines of $\sim$2-7 years, we measure
astrometric distances for 22 late-T and early Y dwarfs, including updated
parallaxes for 18 objects and new parallax measurements for 4 objects. These
parallaxes will make it possible to explore the physical parameter space
occupied by the coldest brown dwarfs. We also present the discovery of 6 new
late-T dwarfs, updated spectra of two T dwarfs, and the reclassification of a
new Y dwarf, WISE J033605.04$-$014351.0, based on Keck/NIRSPEC $J$-band
spectroscopy. Assuming that effective temperatures are inversely proportional
to absolute magnitude, we examine trends in the evolution of the spectral
energy distributions of brown dwarfs with decreasing effective temperature.
Surprisingly, the Y dwarf class encompasses a large range in absolute magnitude
in the near- to mid-infrared photometric bandpasses, demonstrating a larger
range of effective temperatures than previously assumed. This sample will be
ideal for obtaining mid-infrared spectra with the James Webb Space Telescope
because their known distances will make it easier to measure absolute physical
properties.
