Star formation activity beyond the outer Arm I: WISE-selected candidate star-forming regions

Abstract

The outer Galaxy beyond the Outer Arm provides a good opportunity to study star formation in an environment significantly different from that in the solar neighborhood. However, star-forming regions in the outer Galaxy have never been comprehensively studied or cataloged because of the difficulties in detecting them at such large distances. We studied 33 known young star-forming regions associated with 13 molecular clouds at $R_{\mathrm{G}}$ $\ge$ 13.5 kpc in the outer Galaxy with data from the Wide-field Infrared Survey Explorer (WISE) mid-infrared all-sky survey. From their color distribution, we developed a simple identification criterion of star-forming regions in the outer Galaxy with the WISE color. We applied the criterion to all the WISE sources in the molecular clouds in the outer Galaxy at $R_{\mathrm{G}}$ $\ge$ 13.5 kpc detected with the Five College Radio Astronomy Observatory (FCRAO) ${}^{12}$CO survey of the outer Galaxy, of which the survey region is 102${}^{\circ }$.49 $\le$ $l$ $\le$ 141${}^{\circ }$.54, $-$3${}^{\circ }$.03 $\le$ $b$ $\le$ 5${}^{\circ }$.41, and successfully identified 711 new candidate star-forming regions in 240 molecular clouds. The large number of samples enables us to perform the statistical study of star-formation properties in the outer Galaxy for the first time. This study is crucial to investigate the fundamental star-formation properties, including star-formation rate, star-formation efficiency, and initial mass function, in a primordial environment such as the early phase of the Galaxy formation.

54 pages, 16 figures, accepted for publication AJ

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