DUST IN STARBURST GALAXIES

To investigate the nature of starburst dust, we constructed a model of the stars and dust in starburst galaxies and applied it to 30 observe d starburst spectral energy distributions (SEDs). The starburst model was constructed by combining two stellar evolutionary synthesis models with a model describing the radiative transfer of stellar photons thr ough dust. The stellar evolutionary synthesis models were used to comp ute the dust-free SEDs for stellar populations with ages between 1 x 1 0(6) and 15 x 10(9) yr. Using a Monte Carlo radiative transfer model, the effects of dust were computed for average Milky Way (MW) and Small Magellanic Cloud (SMC) dust, two different star/dust geometries, and locally homogeneous or clumpy dust. Using color-color plots, the starb urst model was used to interpret the behavior of 30 starbursts with ap erture-matched UV and optical SEDs (and IR for 19 of the 30) from prev ious studies. From the color-color plots, it was evident that the dust in starbursts has an extinction curve lacking a 2175 Angstrom bump, l ike the SMC curve, and a steep far-UV rise, intermediate between the M W and SMC curves. The star/dust geometry that is able to explain the d istribution of the 30 starbursts in various color-color plots has an i nner dust-free sphere of stars surrounded by an outer star-free shell of clumpy dust. When combined with other work from the literature on t he Orion region and the 30 Dor region of the Large Magellanic Cloud, t his work implies a trend in dust properties with star formation intens ity.