Probing spectral properties of radio-quiet quasars searched for optical microvariability - II

In the context of active galactic nucleus (AGN) unification schemes, rapid variability properties play an important role in understanding any intrinsic differences between sources in different classes. In this respect, any clue based on spectral properties will be very useful toward understanding the mechanisms responsible for the origin of rapid small-scale optical variations or microvariability. Here we have added spectra of 46 radio-quiet quasars (RQQSOs) and Seyfert 1 galaxies to those of our previous sample of 37 such objects, all of which had been previously searched for microvariability. We took new optical spectra of 33 objects and obtained 13 others from the literature. Their H beta and Mg II emission lines were carefully fitted to determine line widths (FWHM) as well as equivalent widths (EW) due to the broad emission-line components. The line widths were used to estimate black hole masses and Eddington ratios, l. Both EW and FWHM are anticorrelated with l. Nearly all trends were in agreement with our previous work, although the tendency for sources exhibiting microvariability to be of lower luminosity was not confirmed. Most importantly, this whole sample of EW distributions provides no evidence for the hypothesis that a weak jet component in radio-quiet AGNs is responsible for their microvariability.