The association of IRAS sources and $\mathsf{^{12}}$CO emission in the outer Galaxy

Abstract

We have revisited the question of the association of CO emission with IRAS sources in the outer Galaxy using data from the FCRAO Outer Galaxy Survey (OGS). The availability of a large-scale high-resolution CO survey allows us to approach the question of IRAS-CO associations from a new direction - namely we examined all of the IRAS sources within the OGS region for associated molecular material. By investigating the association of molecular material with random lines of sight in the OGS region we were able to construct a quantitative means to judge the likelihood that any given IRAS-CO association is valid and to disentangle multiple emission components along the line of sight. The paper presents a list of all of the IRAS-CO associations in the OGS region. We show that, within the OGS region, there is a significant increase (22%) in the number of probable star forming regions over previous targeted CO surveys towards IRAS sources. As a demonstration of the utility of the IRAS-CO association table we present the results of three brief studies on candidate zone-of-avoidance galaxies with IRAS counterparts, far outer Galaxy CO clouds, and very bright CO clouds with no associated IRAS sources. We find that25% of such candidate ZOAGs are Galactic objects. We have discovered two new far outer Galaxy star-forming regions, and have discovered six bright molecular clouds that we believe are ideal targets for the investigation of the earliest stages of sequential star formation around Hii regions. Finally, this paper provides readers with the necessary data to compare other catalogued data sets with the OGS data.