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

TL;DR

This study uses WISE infrared data to identify and catalog over 700 candidate star-forming regions in the outer Galaxy, enabling the first statistical analysis of star formation in this primordial environment.

Contribution

Developed a simple WISE color-based criterion to identify star-forming regions and applied it to discover 711 new candidates in the outer Galaxy, expanding the known sample.

Findings

Identified 711 new candidate star-forming regions.

Enabled statistical analysis of star formation properties in the outer Galaxy.

Provided insights into star formation in early galactic environments.

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 $R_{\rm G}$ $\ge$ 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 $R_{\rm G}$ $\ge$ 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.