Large-scale effects of ionizing feedback
  I discuss recent work on gas expulsion and triggered star formation in, and unbinding of, embedded clusters, by ionizing radiation from O-type stars. Photoionization is not as effective a driver of any of these process as was perhaps once thought. Although structures such as pillars, bubble and champagne flows emerge naturally from the action of ionization on turbulent clouds, the association of stars with such structures does not necessarily imply that they have been triggered. 
James Dale
astro-ph.SR astro-ph.GA