2022ApJ...936..181I

The outer Galaxy beyond the Outer Arm represents a promising opportunity to study star formation in an environment vastly different from the solar neighborhood. In our previous study, we identified 788 candidate star-forming regions in the outer Galaxy (at galactocentric radii R_G ≥ 13.5 kpc) based on the Wide-field Infrared Survey Explorer (WISE) mid-infrared (MIR) all-sky survey. In this paper, we investigate the statistical properties of the candidates and their parental molecular clouds derived from the Five College Radio Astronomy Observatory (FCRAO) CO survey. We show that the molecular clouds with candidates have cloud mass functions with shallower slopes, larger fractions of clouds bound by self-gravity, and a greater density than the molecular clouds without candidates. To investigate the star formation efficiency (SFE) at different R_G, we used two parameters: (1) the fraction of molecular clouds with candidates and (2) the monochromatic MIR luminosities of candidates per parental molecular cloud mass. We did not find any clear correlation between SFE parameters and R_G at R_G of 13.5-20.0 kpc, suggesting that the SFE is independent of environmental parameters such as metallicity and gas surface density, which vary considerably with R_G. Previous studies reported that the SFE per year (SFE/yr) derived from the star formation rate surface density per total gas surface density, H I plus H₂, decreases with increased R_G. Our results might suggest that the decreasing trend is due to a decrease in the conversion of H I gas to H₂ gas.