  While conducting a near-infrared (NIR) survey of ``Digel Clouds'', which are
thought to be located in the extreme outer Galaxy (EOG), Kobayashi & Tokunaga
found star formation activity in ``Cloud 2'', a giant molecular cloud at the
Galactic radius of ~ 20 kpc. Additional infrared imaging showed two embedded
young clusters at the densest regions of the molecular cloud. Because the
molecular cloud is located in the vicinity of a supernova remnant (SNR) HI
shell, GSH 138-01-94, it was suggested that the star formation activity in
Cloud 2 was triggered by this expanding HI shell. We obtained deep J (1.25 um),
H (1.65 um) and K (2.2 um) images of one of the embedded clusters in Cloud 2
with high spatial resolution (FWHM ~0".3) and high sensitivity (K ~ 20 mag, 10
sigma). We identified 52 cluster members. The estimated stellar density (~ 10
pc^{-2}) suggests that the cluster is a T-association. This is the deepest NIR
imaging of an embedded cluster in the EOG. The observed K-band luminosity
function (KLF) suggests that the underlying initial mass function (IMF) of the
cluster down to the detection limit of ~ 0.1 M_sun is not significantly
different from the typical IMFs in the field and in the near-by star clusters.
The overall characteristics of this cluster appears to be similar to those of
other embedded clusters in the far outer Galaxy. The estimated age of the
cluster from the KLF, which is less than 1 Myr, is consistent with the view
that the star formation was triggered by the HI shell whose age was estimated
at 4.3 Myr (Stil & Irwin). The 3-dimensional geometry of SNR shell, molecular
cloud and the embedded cluster, which is inferred from our data, as well as the
cluster age strongly suggest that the star formation in Cloud 2 was triggered
by the SNR shell.
