A Mini X-Ray Survey of Sub-DLAs; Searching for AGNs Formed in
  Protogalaxies
  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
~ 1 arcsec 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 x
10^{44}h^{-2} and 4.2 x 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.
