Dust attenuation in z sim 1 galaxies from Herschel and 3D-HST Hα measurements

We combined the spectroscopic information from the 3D-HST survey with \textit{Herschel} data to characterize the H$\alpha$ dust attenuation properties of a sample of 79 main sequence star-forming galaxies at $z \sim 1$ in the GOODS-S field. The sample was selected in the far-IR, at $\lambda$=100 and/or 160 $\mu$m, and only includes galaxies with a secure H$\alpha$ detection (S/N$>$3). From the low resolution 3D-HST spectra we measured the redshifts and the H$\alpha$ fluxes for the whole sample (a factor of 1/1.2 was applied to the observed fluxes to remove the [NII] contamination). The stellar masses (M$_{\star}$), infrared (L$_{IR}$) and UV luminosities (L$_{UV}$) were derived from the SEDs by fitting multi-band data from GALEX near-UV to SPIRE 500 $\mu$m. We estimated the continuum extinction E$_{star}$(B-V) from both the IRX=L$_{IR}$/L$_{UV}$ ratio and the UV-slope, $\beta$, and found an excellent agreement between the two. The nebular extinction was estimated from comparison of the observed SFR$_{H\alpha}$ and SFR$_{UV}$. We obtained \emph{f}=E$_{star}$(B-V)/E$_{neb}$(B-V)=0.93$\pm$0.06, i.e. higher than the canonical value of \emph{f}=0.44 measured in the local Universe. Our derived dust correction produces good agreement between the H$\alpha$ and IR+UV SFRs for galaxies with SFR$\gtrsim$ 20 M$_{\odot}$/yr and M$_{\star} \gtrsim 5 \times 10^{10}$ M$_{\odot}$, while objects with lower SFR and M$_{\star}$ seem to require a smaller \emph{f}-factor (i.e. higher H$\alpha$ extinction correction). Our results then imply that the nebular extinction for our sample is comparable to that in the optical-UV continuum and suggest that the \emph{f}-factor is a function of both M$_{\star}$ and SFR, in agreement with previous studies.