Self-Regulation of Star Formation in Low-Metallicity Clouds

We investigate the process of self-regulated star formation via the photodissociation of hydrogen molecules in low-metallicity clouds. We evaluate the scale of the influence region for a massive star in low-metallicity gas clouds whose temperatures are between 102 and 104 K. A single O star can photodissociate H2 in the whole of the host cloud. If the metallicity is less than about 10-2.5 of the solar metallicity, the depletion of coolants in the host cloud is very serious, so that the cloud cannot cool in a free-fall time, and subsequent star formation is almost quenched. On the other hand, if the metallicity is greater than about 10-1.5 of the solar metallicity, star formation regulation via photodissociation is not efficient. The typical metallicity when this transition occurs is ~10-2 of the solar metallicity. This indicates that stars do not form efficiently before the metallicity becomes larger than about 10-2 of the solar metallicity, and we consider that this value is the lower limit of the metallicity of luminous objects such as galaxies.