Star Formation and Dust Attenuation Properties in Galaxies from a Statistical UV-to-FIR Analysis
Résumé
We study two galaxy 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 attenuation laws (power law + 2175 Angstroem bump). The Bayesian method allows to estimate statistically 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 an SED analysis if the FIR information is not used. The deduced dispersion is larger than with the FIR data and the distribution is not symetrically 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 UV-selected galaxies have attenuation laws in average similar to the LMC extinction while FIR-selected galaxy 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 parameter b_0 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 be used whenever the FIR information is not available because the resulting Afuv is poorly defined with an uncertainty of about 0.32): A_{FUV} = 1.4168 (FUV-NUV)^2 + 0.3298 (NUV-I)^2 + 2.1207 (FUV-NUV) + 2.7465 (NUV-I) + 5.8408
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