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K.D. Gordon, G.C. Clayton, K.A. Misselt (Louisiana State U.), A.N. Witt (U. of Toledo)
We present a method for calculating the attenuation at a particular wavelength, Att(\lambda), based on the measurement of F(IR)/F(\lambda). We calibrate this method using spectral energy distributions (SEDs) from the PEGASE stellar evolutionary synthesis model and the effects of dust (absorption and scattering) as calculated from our Monte Carlo radiative transfer model. We tested the attenuations predicted from this method for the H\alpha, H\beta, and H\gamma emission lines of 10 starburst galaxies against those calculated using radio observations and found good agreement. The relationship between Att(\lambda) and F(IR)/F(\lambda) is only weakly dependent on the assumed dust grain properties, star/gas/dust geometry, and clumpiness of the dust distribution. In general, the relationship is dependent on the shape (age, metallicity, etc.) of the unattenuated galaxy SED. Starburst galaxies represent a special case where the attenuations at UV wavelengths can be calculated without knowledge of their unattenuated SEDs. We show examples of UV/optical attenuation curves for a few starburst galaxies which illustrate the radiative transfer effects of mixing stars and dust. With proper calibration of this method, it should be applicable to all types of galaxies. Our new method is the only one which uses the observations of a single galaxy to determine that galaxy's UV through near-IR attenuation curve. As a result, it is now possible to accurately disentangle the effects of dust from those of stellar age and metallicity in individual galaxies.
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