The Flux Ratio Method for Determining the Dust Attenuation of Starburst Galaxies

The presence of dust in starburst galaxies complicates the study of theirstellar populations as the dust's effects are similar to those associated withchanges in the galaxies' stellar age and metallicity. This degeneracy can beovercome for starburst galaxies if UV/optical/near-infrared observations arecombined with far-infrared observations. We present the calibration of the fluxratio method for calculating the dust attenuation at a particular wavelength,Att(\lambda), based on the measurement of F(IR)/F(\lambda) flux ratio. Ourcalibration is based on spectral energy distributions (SEDs) from the PEGASEstellar evolutionary synthesis model and the effects of dust (absorption andscattering) as calculated from our Monte Carlo radiative transfer model. Wetested the attenuations predicted from this method for the Balmer emissionlines of a sample starburst galaxies against those calculated using radioobservations and found good agreement. The UV attenuation curves for a handfulof starburst galaxies were calculated using the flux ratio method, and theycompare favorably with past work. The relationship between Att(\lambda) andF(IR)/F(\lambda) is almost completely independent of the assumed dustproperties (grain type, distribution, and clumpiness). For the UV, therelationship is also independent of the assumed stellar properties (age,metallicity, etc) accept for the case of very old burst populations. However atlonger wavelengths, the relationship is dependent on the assumed stellarproperties.