The connection between the sub-mm and the hard X-ray backgrounds is studied by comparing data at 2–10 keV and at 850 \mu m for a sample of 34 sources at fluxes ( or limiting fluxes ) which resolve most of the background in the two bands .
These data were obtained with new SCUBA observations and by correlating data sets available from the literature .
None of the 11 hard X-ray ( 2–10 keV ) sources has a counterpart at 850 \mu m , with the exception of a faint Chandra source , which is a candidate type 2 QSO at high redshift .
These data indicate that 2–10 keV sources brighter than 10 ^ { -15 } erg~ { } s ^ { -1 } cm ^ { -2 } , which make at least 75 % of the background in this band , contribute for less than 7 % to the submillimetric background .
Out of the 24 SCUBA sources 23 are undetected by Chandra .
These data indicate that most of these SCUBA sources must be powered either by starburst activity , or by an AGN which is obscured by a column N _ { H } > 10 ^ { 25 } cm ^ { -2 } , with a reflection efficiency in the hard X-rays significantly lower than 1 % in most cases .