Study of a homogeneous QSO sample: relations between the QSO and its
  host galaxy
  We analyse a sample of 69 QSOs which have been randomly selected in a
complete sample of 104 QSOs (R<18, 0.142 < z < 0.198). 60 have been observed
with the NTT/SUSI2 at La Silla, through two filters in the optical band (WB#655
and V#812), and the remaining 9 are taken from archive databases. The filter
V#812 contains the redshifted Hbeta and forbidden [OIII] emission lines, while
WB#655 covers a spectral region devoid of emission lines, thus measuring the
QSO and stellar continua. The contributions of the QSO and the host are
separated thanks to the MCS deconvolution algorithm, allowing a morphological
classification of the host, and the computation of several parameters such as
the host and nucleus absolute V-magnitude, distance between the luminosity
center of the host and the QSO, and colour of the host and nucleus. We define a
new asymmetry coefficient, independent of any galaxy models and well suited for
QSO host studies. The main results from this study are: (i) 25% of the total
number of QSO hosts are spirals, 51% are ellipticals and 60% show signs of
interaction; (ii) Highly asymmetric systems tend to have a higher gas
ionization level (iii) Elliptical hosts contain a substantial amount of ionized
gas, and some show off-nuclear activity. These results agree with hierarchical
models merger driven evolution.
