Identifying the Lens Galaxy B1152+199 as a Ghostly Damped Lyman Alpha
  System by the Cosmic Origins Spectrograph
  Strong quasar-galaxy lensing provides a powerful tool to probe the
inter-stellar medium (ISM) of the lens galaxy using radiation from the
background quasar. Using the Cosmic Origins Spectrograph (COS) on board the
Hubble Space Telescope, we study the cold ISM properties of the lens galaxy in
B1152+199 at a redshift of z=0.4377. Since existing optical extinction and
X-ray absorption measurements of the lens have revealed a large amount of cold
ISM, we expected to detect a damped Lya absorption (DLA) system in the near
ultraviolet spectrum; however, our upper limit on the HI column density is
several orders of magnitude below the expectation. We also marginally detect OI
and CII absorption lines associated with the lens galaxy in the COS spectrum.
Thus, the lens galaxy is identified as a ghostly DLA system, and further
investigations of these ghostly DLA systems would be important to characterize
the biases of using DLAs to probe the matter density of the universe. Although
preliminary, the most likely explanation of the non-detection of the DLA is
because of the Lya emission of the lens galaxy that fills in the absorption
trough, with a Lya luminosity of 4e42 erg/s.
