The large gas and dust reservoirs of submm galaxies ( SMGs ) could potentially provide ample fuel to trigger an Active Galactic Nucleus ( AGN ) , but previous studies of the AGN fraction in SMGs have been controversial largely due to the inhomogeneity and limited angular resolution of the available submillimeter surveys .
Here we set improved constraints on the AGN fraction and X-ray properties of the SMGs with ALMA and Chandra observations in the Extended Chandra Deep Field-South ( E-CDF-S ) .
This study is the first among similar works to have unambiguously identified the X-ray counterparts of SMGs ; this is accomplished using the fully submm-identified , statistically reliable SMG catalog with 99 SMGs from the ALMA LABOCA E-CDF-S Submillimeter Survey ( ALESS ) .
We found 10 X-ray sources associated with SMGs ( median redshift z = 2.3 ) , of which 8 were identified as AGNs using several techniques that enable cross-checking .
The other 2 X-ray detected SMGs have levels of X-ray emission that can be plausibly explained by their star-formation activity .
6 of the 8 SMG-AGNs are moderately/highly absorbed , with N _ { H } > 10 ^ { 23 } { cm ^ { -2 } } .
An analysis of the AGN fraction , taking into account the spatial variation of X-ray sensitivity , yields an AGN fraction of 17 ^ { +16 } _ { -6 } \% for AGNs with rest-frame 0.5–8 keV absorption-corrected luminosity \geqslant 7.8 \times 10 ^ { 42 } erg s ^ { -1 } ; we provide estimated AGN fractions as a function of X-ray flux and luminosity .
ALMA ’ s high angular resolution also enables direct X-ray stacking at the precise positions of SMGs for the first time , and we found 4 potential SMG-AGNs in our stacking sample .