A glance at the host galaxy of high-redshift quasars using strong damped
  Lyman-alpha systems as coronagraphs
  We searched quasar spectra from the SDSS-III Baryon Oscillation Spectroscopic
Survey (BOSS) for the rare occurrences where a strong damped Lyman-alpha
absorber (DLA) blocks the Broad Line Region emission from the quasar and acts
as a natural coronagraph to reveal narrow Ly\alpha\ emission from the host
galaxy. We define a statistical sample of 31 DLAs in Data Release 9 (DR9) with
log N(HI) > 21.3 cm^-2 located at less than 1500 km s^-1 from the quasar
redshift. In 25% (8) of these DLAs, a strong narrow Ly\alpha\ emission line is
observed with flux ~25 x 10^-17 erg s^-1 cm^-2 on average. For DLAs without
this feature in their troughs, the average 3-\sigma\ upper limit is < 0.8 x
10^-17 erg s^-1 cm^-2. Our statistical sample is nearly 2.5 times larger than
the anticipated number of intervening DLAs in DR9 within 1500 km s^-1 of the
quasar redshift. We also define a sample of 26 DLAs from DR9 and DR10 with
narrow Ly\alpha\ emission detected and no limit on the HI column density to
better characterize properties of the host galaxy emission. Analyzing the
statistical sample, we do not find substantial differences in the kinematics,
metals, or reddening for the two populations with and without emission
detected. The highly symmetric narrow Ly\alpha\ emission line profile centered
in the HI trough indicates that the emitting region is separate from the
absorber. The luminosity of the narrow Ly\alpha\ emission peaks is intermediate
between that of Lyman-alpha emitters and radio galaxies, implying that the
Ly\alpha\ emission is predominantly due to ionizing radiation from the AGN.
Galaxies neighboring the quasar host are likely responsible for the majority (>
75%) of these DLAs, with only a minority (< 25%) arising from HI clouds located
in the AGN host galaxy.
