The dangers of being trigger--happy

We examine the evidence offered for triggered star formation against the backdrop provided by recent numerical simulations of feedback from massive stars at or below giant molecular cloud sizescales. We compile a catalogue of sixty--seven observational papers, mostly published over the last decade, and examine the signposts most commonly used to infer the presence of triggered star formation. We then determine how well these signposts perform in a recent suite of hydrodynamic simulations of star formation including feedback from O--type stars performed by Dale et al (2012a, b, 2013a, b, 2014). We find that none of the observational markers improve the chances of correctly identifying a given star as triggered by more than factors of two at most. This limits the fidelity of these techniques in interpreting star formation histories. We therefore urge caution in interpreting observations of star formation near feedback--driven structures in terms of triggering.