A comparative analysis of the long-term optical variability characteristics of narrow and broad-line Seyfert 1 galaxies at z > 0.8

RESUMO

We present the results on a comparative analysis of the long-term optical variability characteristics of high-redshift narrow-line Seyfert 1 (NLSy1) galaxies and broad-line Seyfert 1 (BLSy1) galaxies. Our sample spanning the redshift range of $0.8 < z < 2.6$, comprises 2490 NLSy1 and 2490 BLSy1 galaxies matched in the optical brightness$-$redshift plane. We used V-band data from the Catalina Real-Time Transient Survey covering a baseline of 5$-$9 years, and g, r, and i-band data from the Zwicky Transient Facility spanning 5 to 6 years. To characterise variability we estimated the amplitude of variability ($\sigma_m$). We found that NLSy1 galaxies generally exhibit lower $\sigma_m$ compared to BLSy1 galaxies. In both the NLSy1 and BLSy1 galaxy samples, we observed a wavelength dependent variability using data from Zwicky Transient Facility, with $\sigma_m$ gradually increasing towards shorter wavelengths. We found an anti-correlation between $\sigma_m$ and Eddington ratio in the g, r, and i bands for BLSy1 galaxies, whereas this anti-correlation is observed only in the r and i bands for NLSy1 galaxies. For both NLSy1 and BLSy1 galaxies, we found no correlation between $\sigma_m$ in g, r, and i bands and black hole mass. In both the samples, we found that $\sim$90\% of the sources showed a bluer when brighter trend. We found no significant time lag between variations in g and r bands in both BLSy1 and NLSy1 galaxies. The observed long-term trends in the optical light curves of our high redshift sample of BLSy1 and NLSy1 galaxies could be driven by variations in the accretion disk.