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Herschel reveals the obscured star formation in HiZELS Hα emitters at z=1.47

We describe the far-infrared (FIR; rest-frame 8--1000μm) properties of a sample of 443 Hα-selected star-forming galaxies in the COSMOS and UDS fields detected by the HiZELS imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select Hα (and [OII] if available) emitters in a narrow redshift slice at z = 1.47+/-0.02. We use a stacking approach in Spitzer, Herschel (from PEP and HerMES surveys) and AzTEC images to describe their typical FIR properties. We find that HiZELS galaxies with observed Hα luminosities of ~ 10^{8.1-9.1} Lo have bolometric FIR luminosities of typical LIRGs, L_FIR ~ 10^{11.48+/-0.05} Lo. Combining the Hα and FIR luminosities, we derive median SFR = 32+/-5 Mo/yr and Hα extinctions of A(Hα) = 1.0+/-0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass (M*) to A(Hα) relations and the little or no evolution up to z = 1.47. For HiZELS galaxies, we provide an empirical parametrisation of the SFR as a function of (u-z)_rest colours and 3.6μm photometry. We find that the observed Hα luminosity is a dominant SFR tracer when (u-z)_rest ~< 0.9 mag or when 3.6μm photometry > 22 mag (Vega) or when M* < 10^9.7 Mo. We do not find any correlation between the [OII]/Hα and FIR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions. The luminosity-limited HiZELS sample tends to lie above of the so-called `main sequence' for star-forming galaxies, especially at low M*. This work suggests that obscured star formation is linked to the assembly of M*, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.