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

Abstract

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.

arXiv commentAccepted at Astrophysics and Space Science