Ghostly Damped Ly$\alpha$ Systems: Tracers of Gas Flows in the Close
  Vicinity of Quasars ?
  We have searched the Sloan Digital Sky Survey Data Release 12 for ghostly
Damped Ly$\alpha$ (DLA) systems. These systems, located at the redshift of the
quasars, show strong absorption from low-ionization atomic species but reveal
no HI Ly$\alpha$ absorption. Our search has, for the first time, resulted in a
sample of 30 homogeneously selected ghostly DLAs with $z_{\rm QSO}$$>$2.0.
Thirteen of the ghostly DLAs exhibit absorption from other HI Lyman series
lines. The lack of Ly$\alpha$ absorption in these absorbers is consistent with
them being dense and compact with projected sizes smaller than the broad line
region (BLR) of the background quasar. Although uncertain, the estimated median
HI column density of these absorbers is log$N$(HI)$\sim$21.0. We compare the
properties of ghostly DLAs with those of eclipsing DLAs that are high column
density absorbers, located within 1500 km/s of the quasar emission redshift and
showing strong Ly$\alpha$ emission in their DLA trough. We discover an apparent
sequence in the observed properties of these DLAs with ghostly DLAs showing
wider HI kinematics, stronger absorptions from high-ionization species, CII and
SiII excited states, and higher level of dust extinction. Since we estimate
that all these DLAs have similar metallicities, log$Z/Z_{\odot}$$\sim$$-$1.0,
we conclude that ghostly DLAs are part of the same population as eclipsing
DLAs, except that they are denser and located closer to the central active
galactic nuclei (AGNs).
