Extreme Outer Galaxy: A Laboratory of Star Formation in an Early Epoch of Galaxy Formation

The extreme outer Galaxy (EOG) has a very different environment from that in the solar neighborhood, with low metallicity (less than -0.5 dex), much lower gas density, and small or no perturbation from spiral arms. The EOG is an excellent laboratory for the study of the star formation processes that happened during the formation period of the Galaxy. In particular, the study of the EOG may shed light, on the origin and role of the thick disk, whose metallicity range matches well with that, of the EOG. We show an example of a molecular cloud in the EOC (Digel's Cloud 2), which is located at RG similar to 20 kpc beyond the Outer arm. Based on our NIR and (CO)-C-12 data as well as H I. radio continuum, and IRAS data in the archives, we examined the detailed star formation processes in this unique environment, especially the supernova triggered star formation, which should have been the major star formation mode during the halo and thick disk formation.