  We have identified a previously unrecognized population of very compact,
embedded low-mass Galactic stellar clusters. These tight (r$ \approx $0.14 pc)
groupings appear as bright singular objects at the few arcsec resolution of the
Spitzer Space Telescope at 8 and 24 $\mu$m but become resolved in the
sub-arcsecond UKIDSS images. They average six stars per cluster surrounded by
diffuse infrared emission and coincide with 100 -- 300 M$_{\sun}$ clumps of
molecular material within a larger molecular cloud. The magnitudes of the
brightest stars are consistent with mid- to early-B stars anchoring $\sim$80
M$_{\sun}$ star clusters. Their evolutionary descendants are likely to be
Herbig Ae/Be pre-main sequence clusters. These ultra-compact embedded clusters
(UCECs) may fill part of the low-mass void in the embedded cluster mass
function. We provide an initial catalog of 18 UCECs drawn from infrared
Galactic Plane surveys.

Astrophysics of Galaxies