On the redshift of the gamma-ray blazar PKS 0447-439: Optical
  spectroscopy using Gemini observations with high S/N ratio
  The BL-Lac blazar PKS 0447-439 was detected at very high energy gamma-rays by
HESS following the discovery by Fermi-LAT. The lack of both emission and
absorption lines in BL-Lacs make the estimation of their redshifts very
difficult. Modeling the drop in gamma-ray spectra it was possible to have an
estimation of redshift for PKS 0447-439 of z approx 0.2, which is compatible
with the value z=0.205 reported by the identification of Ca II absorption lines
in optical spectra. By the identification of a weak line of Mg II using spectra
with average signal-to-noise S/N approx 80, it has been recently reported a
lower limit for the redshift of this blazar of z<=1.246. Triggered by this
controversy, we have proposed new optical observations with the Gemini South
telescope to perform further spectroscopic analysis with very high S/N ratio
(approx 200-500). In this work we present a new optical spectrum of PKS
0447-439, and report on the analysis and results of such observations. Even
with this significantly high quality signal we were not able to identify any
spectral features to allow an estimation of the redshift. In agreement with
other recent studies, we identify the Mg II line reported previously as
originated in the Earth's atmosphere, and conclude the lower limit of the
redshift is incorrect. More interestingly, we could not identify the Ca II
absorption lines used to report a redshift of 0.205.
