Triggered Star Formation in the W5 H ii Region

Abstract

Young, massive stars can have a profound effect on the surrounding interstellar medium. The triggering of star formation by an H ii region expanding into nearby molecular material is an example of this type of interaction. This paper presents a multiwavelength study of the W5 star-forming region investigating the possibility of triggered star formation. The ionizing sources and the morphologies of the ionized and molecular gas and the dust are examined. A population of YSOs is identified. Statistical evidence for triggering of these YSOs is discussed in terms of the spatial dependence of the star formation efficiency and the clustering and correlation of the YSO sources with respect to the molecular gas and the H ii region. Evidence for direct interactions between the components is discussed, on both large scales and the scale of individual objects. Timescales for the expansion of the H ii region, triggering processes, and the ages of the YSOs are compared to establish a plausible sequence of events.