The International Liquid Mirror Telescope project: optical quality tests and prospective detection of multiply imaged quasars

The International Liquid Mirror Telescope (ILMT) project is a joint collaboration
between different universities and research institutes in Belgium, Canada, India
and Poland, for the design, construction and operation of a 4 meter liquid mirror
telescope at the Devasthal Observatory (India).
In the framework of the present thesis, we have contributed to the development
of the ILMT. We have namely designed and manufactured an innovative instru-
ment capable of measuring the optical quality of the primary mirror that may
be affected by the propagation of wavelets on the mercury layer. The instrument
is composed of a laser source, emitting a beam whose reflection on the mirror is
modulated by slope variations induced by the wavelets. Preliminary tests were
carried out showing the validity of the method for on site testing of the mirror.
The ILMT has been designed to perform a photometric variability survey of
a narrow strip of sky, making it very suitable for the detection and follow-up of
photometrically variable sources such as supernovae and quasars.
In the second part of this thesis, we present an estimate of the number of QSOs
to be detected within the ILMT survey, and of the expected number of multiply
imaged sources among these caused by the presence of a deflector near the lines-of-
sight. We have studied the impact of various parameters on the expected number
of detected gravitational lens systems, such as the instrumental resolution of the
telescope, the galaxy population type(s) and corresponding lensing model(s), and
the cosmological parameters.
The statistical sample of multiply imaged QSOs is intended to be used as
a cosmological probe. In order to make a sensitivity comparison between vari-
ous modelling approaches, we introduce a new formalism to estimate the lensing
probabilities, based on the joined probability density of the observed QSOs.
This new formalism allows to calculate three probability densities: that asso-
ciated with the optical depth distribution, as well as those related to the deflector
and the lensed source redshift distributions. For the case of FLRW universes, we
compare the sensitivity of these distributions as a function of the cosmological
mass density.