First gravitational lensing mass estimate of a damped Lyman-alpha galaxy
  at z=2.2
  We present the first lensing total mass estimate of a galaxy, at redshift
2.207, that acts as a gravitational deflector and damped Lyman-alpha absorber
on the background QSO SDSS J1135-0010, at redshift 2.888. The remarkably small
projected distance, or impact parameter, between the lens and the source has
been estimated to be 0.8 +/- 0.1 kpc in a recent work. By exploiting the Sloan
Digital Sky Survey database, we establish a likely lensing magnification signal
in the photometry of the QSO. This is determined to be 2.2 mag brighter (or 8
times more luminous) than the median QSO at comparable redshifts. We describe
the total mass distribution of the lens galaxy with a one-component singular
isothermal sphere model and contrast the values of the observed and
model-predicted magnification factors. For the former, we use conservatively
the photometric data of the 95% of the available distant QSO population. We
estimate that the values of the lens effective velocity dispersion and
two-dimensional total mass, projected within a cylinder with radius equal to
the impact parameter, are included between 60 and 170 km/s and 2.1 x 10^9 and
1.8 x 10^10 M_Sun, respectively. We conclude by remarking that analyses of this
kind are crucial to exploring the relation between the luminous and dark matter
components of galaxies in the high-redshift Universe.
