ARE NUCLEAR HOT-SPOTS IN GALAXIES SITES OF SEQUENTIAL STAR-FORMATION

We investigate self-regulated propagation of star formation, which is one of the possible scenarios of star formation in molecular clouds fr agmented into cold dense structures with masses lying near the Jeans l imit. Strong ultraviolet (UV) radiation from newborn massive stars com presses nearby dense inhomogeneities, triggering further star formatio n. Once initiated, the star formation wave propagates with a velocity determined by the parameters of cloud inhomogeneities. The total UV fl ux increases as a result of continued star formation leading to enhanc ed heating and evaporation of protostellar inhomogeneities. Once the U V flux reaches a critical value, propagation of star formation has to stop. Thus the star formation in such a scenario has a built-in self-r egulatory mechanism. The nuclear hot spots in galaxies are explained h ere as sites of self-regulated star formation activity with the UV flu x serving as the trigger and regulator. We determine theoretically an integral stellar spectrum for this scenario and compare it with the re sults for the instantaneous burst scenario. The observed optical color s and low equivalent widths of hot spots cannot be explained with an i nstantaneous burst, but agree well with self-regulated sequential star formation lasting for a few to several tens of million years.