Are Nuclear Hot Spots in Galaxies Sites of Sequential Star Formation?

Abstract

We investigate self-regulated propagation of stars formation, which is one of the possible scenarios of stars formation in molecular clouds fragmented into cold dense structures with masses lying near the Jeans limit. Strong ultraviolet (UV) radiation from newborn massive stars compresses nearby dense inhomogeneities, triggering further str formation. Once initiated, the star formation wave propagates with a velocity determined by the parameters of cloud inhomogeneities. The total UV flux increases as a result of continued star formation leading to enhances heating and evaporation of protostellar inhomogeneities. Once the UV flux reaches a critical value, propagation of star formation has to stop. Thus the star formation in such scenario has a built-in self-regulatory mechanism. The nuclear hot spots in galaxies are explained here as sites of self-regulated star formation activity with the UV flux serving as the trigger and regulator. We determine theoretically an integral stellar spectrum with the scenario and compare it with the results for the instantaneous burst scenario. The observed optical colors and low equivalent widths of hot spots cannot be explained with an instantaneous burst, but agree well with self-regulated sequential stars formation lasting for a few to several tens of million years.