Analysis of interacting and isolated quasars
  The main goal of this study was to determine the effects on equivalent widths
(EWs) of some spectral lines produced in the quasars by the presence of
surrounding galaxies. To carry this out, a sample of 4663 quasars (QSOs) in the
redshift range of 0.20 to 0.40 from the Sloan Digital Sky Survey--Data Release
7 was analyzed. Three QSO sub-samples were defined, taking into account the
projected separations and radial velocity differences with neighboring
galaxies. In this way, we utilized two sub-samples of QSOs with strong and weak
galaxy interactions, with projected separations smaller than 70 kpc, and
between 70 and 140 kpc, respectively, and with radial velocity differences less
than $5000~$\kms. These sub-samples were compared with isolated QSOs defined as
having greater projected separations and radial velocity differences to the
galaxies. From a statistical study of the EWs of relevant spectral lines in the
QSOs, we show an increment of the EWs of about 20\% in the [OIII]4959,5007
lines and 7\% in H$_\alpha$ for QSOs with stronger galaxy interactions relative
to the isolated QSOs. These results indicate that some line EWs of QSOs could
be marginally influenced by the environment and that they are not affected by
the emission of the host galaxy, which was estimated to be around 10\% of the
total emission. Furthermore, in order to gain a better understanding of the
origin of the H$_{\alpha}$ emission line, we performed broad and narrow line
decomposition in 100 QSOs in the restricted Sint sub-sample and also 100
randomly selected QSOs in the Iso sub-sample. When these QSOs were compared,
the narrow component remained constant whereas the broad component was
incremented. Our results, which reveal slight differences in EWs of some
emission lines, suggest that galaxy interactions with QSOs may affect the QSO
activity.
