A significant fraction of the sub-damped Lyman-alpha ( sub-DLA ) absorption systems in quasar spectra appear to be metal-rich , many with even super-solar element abundances .
This raises the question whether some sub-DLAs may harbor active galactic nuclei ( AGN ) since supersolar metallicities are observed in AGN .
Here we investigate this question based on a mini-survey of 21 quasars known to contain sub-DLAs in their spectra .
The X-ray observations were performed with the Chandra X-ray Observatory .
In cases of no detection we estimated upper limits of the X-ray luminosities of possible AGNs at the redshifts of the sub-DLAs .
In six cases we find possible X-ray emission within \sim 1 ^ { \prime \prime } of the background quasar consistent with the presence of a nearby X-ray source .
If these nearby X-ray sources are at the redshifts of the sub-DLAs , their estimated 0.2 - 10 keV luminosities range between 0.8 \times 10 ^ { 44 } h ^ { -2 } and 4.2 \times 10 ^ { 44 } h ^ { -2 } erg s ^ { -1 } , thus ruling out a normal late-type galaxy origin , and suggesting that the emission originates in a galactic nucleus near the center of a protogalaxy .
The projected distances of these possible nearby X-ray sources from the background quasars lie in the range of 3–7 h ^ { -1 } kpc , consistent with our hypothesis that they represent AGNs centered on the sub-DLAs .
Deeper follow-up X-ray and optical observations are required to confirm the marginal detections of X-rays from these sub-DLA galaxies .