An extended Herschel drop-out source in the center of AS1063, a 'normal'
  dusty galaxy at z=6.1 or SZ substructures?
  In the course of our 870um APEX/LABOCA follow up of the Herschel Lensing
Survey we have detected a source in AS1063 (RXC J2248.7-4431), that has no
counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel
'drop-out' with S_870/S_500>0.5. The 870um emission is extended and centered on
the brightest cluster galaxy suggesting either a multiply imaged background
source or substructure in the Sunyaev-Zel'dovich (SZ) increment due to
inhomogeneities in the hot cluster gas of this merging cluster. We discuss both
interpretations with emphasis on the putative lensed source. Based on the
observed properties and on our lens model we find that this source could be the
first SMG with a moderate far infrared luminosity (L_FIR<10^12 L_sol) detected
so far at z>4. In deep HST observations we identified a multiply imaged z~6
source and we measured its spectroscopic redshift z=6.107 with VLT/FORS. This
source could be associated with the putative SMG but it is most likely offset
spatially by 10-30kpc and they could be interacting galaxies. With a FIR
luminosity in the range [5-15]x10^{11} L_sol corresponding to a star formation
rate in the range [80-260]M_sol/yr, this SMG would be more representative than
the extreme starbursts usually detected at z>4. With a total magnification of
~25 it would open a unique window to the 'normal' dusty galaxies at the end of
the epoch of reionization.
