A third HI 21-cm absorption system in the sight-line of MG J0414+0534: A
  redshift for Object X?
  We report the detection of a third HI 21-cm absorber in the sight-line
towards the z=2.64 quasar MG J0414+0534 (4C +05.19). In addition to the
absorption at the host redshift and in the z=0.96 gravitational lens, we find,
through a decimetre-wave spectral scan towards this source, strong absorption
at z=0.38. We believe this may be associated with "Object X", an additional
feature apparent in the field of the lensing galaxy and lensed images, on the
basis of its close proximity to the quasar images and the possible detection of
the [OIII] doublet in a published optical spectrum. If real, the strength of
the [OIII] emission would suggest the presence of an active galactic nucleus,
or a gas-rich galaxy undergoing rapid star formation, either of which is
consistent with the strong outflows apparent in the 21-cm spectrum. Although
this is the strongest intervening 21-cm absorber yet found, simultaneous
observations failed to detect any of the 18-cm OH lines at the 21-cm redshift.
This suggests that, as for the lensing galaxy, this is not the primary location
of the intervening material responsible for the very red colour of MG
J0414+0534.
