HerMES: The Rest-Frame UV Emission and A Lensing Model for the z=6.34 Luminous Dusty Starburst Galaxy HFLS3

We discuss the restframe UV emission from the starbursting galaxy HFLS3 at z=6.34, discovered in Herschel/SPIRE data due to its red color in the submm wavelengths from 250-500 um. The apparent inst. SFR of HFLS3 inferred from the total FIR luminosity measured with over 15 photometric data points between 100 to 1000 um is 2900 Msun/yr. Keck/NIRC2 Ks band adaptive optics imaging data showed two potential NIR counterparts near HFLS3. Previously, the northern galaxy was taken to be in the foreground at z=2.1 while the southern galaxy was assumed to HFLS3's NIR counterpart. New HST/WFC3 and ACS imaging data show both optically bright galaxies are in the foreground at z<6. A new lensing model based on HST data and mm-wave continuum emission yields a magnification of 2.2+/-0.3. The lack of multiple imaging constrains the lensing magnification to be lower than either 2.7 or 3.5 at the 95% confidence level for the two scenarios, which attribute one or two components to HFLS3 in the source plane. Correcting for gravitational lensing, the inst. SFR is 1320 Msun/yr with the 95% confidence lower limit around 830 Msun/yr. Using models for the restframe UV to FIR SED, the ave. SFR over the last 100 Myr is around 660 Msun/yr. The dust and stellar masses of HFLS3 from the same SED models are 3x10^8 Msun and ~5x10^10 Msun, respectively, with large systematic uncertainties on assumptions related to the SED model. With HST/WFC3 images we also find diffuse NIR emission about 0.5" (~3 kpc) SW of HFLS3 that remains undetected in the ACS data. The emission has a photometric redshift consistent with either z~6 or a dusty galaxy template at z~2. If at the same redshift as HFLS3 the detected diffuse emission could be part of the complex merger system that could be triggering the starburst. Alternatively, it could be part of the foreground structure at z~2.1 that is responsible for lensing of HFLS3.