Eclipsing damped Ly$\alpha$ systems in the Sloan Digital Sky Survey Data
  Release 12
  We present the results of our automatic search for proximate damped
Ly$\alpha$ absorption (PDLA) systems in the quasar spectra from the Sloan
Digital Sky Survey Data Release 12. We constrain our search to those PDLAs
lying within 1500 km s$^{-1}$ from the quasar to make sure that the broad DLA
absorption trough masks most of the strong Ly$\alpha$ emission from the broad
line region (BLR) of the quasar. When the Ly$\alpha$ emission from the BLR is
blocked by these so-called eclipsing DLAs, narrow Ly$\alpha$ emission from the
host galaxy could be revealed as a narrow emission line (NEL) in the DLA
trough. We define a statistical sample of 399 eclipsing DLAs with
log$N$(HI)$\ge$21.10. We divide our statistical sample into three subsamples
based on the strength of the NEL detected in the DLA trough. By studying the
stacked spectra of these subsamples, we found that absorption from high
ionization species are stronger in DLAs with stronger NEL in their absorption
core. Moreover, absorption from the excited states of species like SiII are
also stronger in DLAs with stronger NEL. We also found no correlation between
the luminosity of the Ly$\alpha$ NEL and the quasar luminosity. These
observations are consistent with a scenario in which the DLAs with stronger NEL
are denser and physically closer to the quasar. We propose that these eclipsing
DLAs could be the product of the interaction between infalling and outflowing
gas. High resolution spectroscopic observation would be needed to shed some
light on the nature of these eclipsing DLAs.
