Star Formation and Dust Attenuation Properties in Galaxies from a Statistical UV-to-FIR Analysis

We study two galaxies samples selected in ultraviolet (UV) and in far infrared (FIR) for which the spectral energy distributions (SEDs) from the far UV (FUV) to the FIR are available. We compare the observed SEDs to modelled SEDs with several star formation histories (SFHs; decaying star formation rate plus burst) and dust attenuation laws (power law + 2175Å bump). The Bayesian method allows to estimate statiscally the best parameters by comparing each observed SED to the full set of 82800 models. We reach the conclusion that the UV dust attenuation cannot be estimated correctly from SED analysis if the FIR information is not used. The dispersion is larger than with the FIR data and the distribution is not symmetrically distributed about zero: there is an over-estimation for UV-selected galaxies and an under-estimation for FIR-selected galaxies. The output from the analysis process suggests that UVselected galaxies have attenuation laws in average similar to the LMC extinction law while FIR-selected galaxies attenuation laws more resemble the MW extinction law. The dispersion about the average relation in the Log(Fdust/FFUV ) vs. FUV −NUV diagram (once the main relation with FUV − NUV is accounted for) is explained by two other parameters: the slope of the attenuation law and the instantaneous birthrate parameters b0 for UV-selected galaxies and the same ones plus the strength of the bump for the FIR-selected galaxies. We propose a recipe to estimate the UV dust attenuation for UV-galaxies only (that should only be used whenever the FIR information is not available because the resulting AFUV is poorly defined with an uncertainty of about 0.32): AFUV = 1.4168(FUV − NUV ) 2 + 0.3298(NUV − I) + 2.1207(FUV −NUV ) + 2.7465(NUV − I) + 5.8408.