Optical spectral characterization of the the TeV extreme blazar 2WHSP
  J073326.7+515354
  The emission from the relativistic jets in blazars usually outshines their
host galaxies, challenging the determination of their distances and the
characterization of the stellar population. The situation becomes more
favorable in the case of the extreme blazars (EHBLs), for which the bulk of the
emission of the relativistic jets is emitted at higher energies, unveiling the
optical emission from the host galaxy. The distance determination is
fundamental for the study of the intrinsic characteristics of the blazars,
especially to estimate the intrinsic gamma-ray spectra distorted due to the
interaction with the Extragalactic Background Light. In this work we report on
the properties of 2WHSP~J073326.7+515354 host galaxy in the optical band, which
is one of the few EHBLs detected at TeV energies. We present the first
measurement of the distance of the source, $\mathrm{z}=0.06504\pm0.00002$
(velocity dispersion $\sigma=237 \pm 9\,\mathrm{km s^{-1}}$). We also perform a
detailed study of the stellar population of its host galaxy. We find that the
mass-weighted mean stellar age is $11.72\pm0.06\,\mathrm{Gyr}$ and the mean
metallicity $[M/H]=0.159 \pm 0.016$. In addition, a morphological study of the
host galaxy is also carried out. The surface brightness distribution is
modelled by a composition of a dominant classical bulge ($R_e=3.77\pm1\arcsec $
or equivalently 4.74~kpc) plus an unresolved source which corresponds to the
active nucleus. The black hole mass is estimated using both the mass relation
with the velocity dispersion and the absolute magnitude from the bulge yielding
comparable results: $(4.8\pm0.9)\times10^8\,M_{\odot}$ and
$(3.7\pm1.0)\times10^8\,M_{\odot}$, respectively.
