The Structure and Star Formation History of NGC 5461

We compute photoionization models for the giant extragalactic H II region NGC5461, and compare their predictions to several observational constraints. Sincewe aim at reproducing not only the global properties of the region, but itslocal structure also, the models are constrained to reproduce the observeddensity profile, and our analysis takes into consideration the bias introducedby the shapes and sizes of the slits used by different observers. We find thatan asymmetric nebula with a gaussian density distribution, powered by a youngburst of 3.1 Myr, satisfactorily reproduces most of the constraints, and thatthe star-formation efficiency inferred from the model agrees with currentestimates. Our results strongly depend on the assumed density law, sinceconstant density models overestimate the hardness of the ionizing field,affecting the deduced properties of the central stellar cluster. We illustratethe features of our best model, and discuss the possible sources of errors anduncertainties affecting the outcome of this type of studies.Comment: 33 pages (LaTeX), 3 .eps figures. to be published in ApJ, May 200