STAR FORMATION IN LUMINOUS H II REGIONS IN M33

We present a multiwavelength (ultraviolet, infrared, optical, and CO) study of a set of luminous H II regions in M33: NGC 604, NGC 595, NGC 592, NGC 588, and IC131. We study the emission distribution in the interiors of the H II regions to investigate the relation between the dust emission at 8 mu m and 24 mu m and the location of the massive stars and gas. We find that the 24 mu m emission is closely related to the location of the ionized gas, while the 8 mu m emission is more related to the boundaries of the molecular clouds consistently with its expected association with photodissociation regions. Ultraviolet emission is generally surrounded by the H alpha emission. For NGC 604 and NGC 595, where CO data are available, we see a radial gradient of the emission distribution at the wavelengths studied here: from the center to the boundary of the H II regions we observe ultraviolet, H alpha, 24 mu m, 8 mu m, and CO emission distributions. We quantify the star formation for our H II regions using the integrated fluxes at the set of available wavelengths, assuming an instantaneous burst of star formation. We show that a linear combination of 24 mu m and H alpha emission better describes the star formation for these objects than the dust luminosities by themselves. For NGC 604, we obtain and compare extinction maps derived from the Balmer decrement and from the 24 mu m and H alpha emission line ratio. Although the maps show locally different values in extinction, we find similar integrated extinctions derived from the two methods. We also investigate here the possible existence of embedded star formation within NGC 604.