Estimating the masses of narrow line Seyfert 1 galaxies using damped random walk method

Abstract

Narrow-line Seyfert 1 galaxies (NLSy1s) are a subclass of active galactic nuclei (AGNs), commonly associated with rapidly accreting, relatively low-mass black holes (106 –108 M) hosted in spiral galaxies. Although typically considered to have high Eddington ratios, recent observations, particularly of γ-ray-emitting NLSy1s, have raised questions about their true black hole masses, with some estimates approaching those of Broad-line Seyfert 1 (BLSy1) systems. In this work, we present the recalibrated mass estimations for a large sample of NLSy1 galaxies with z < 0 . 8. We apply the damped random walk (DRW) formalism to a comparison set of 1141 NLSy1 and 1143 BLSy1 galaxies, matched in redshift and bolometric luminosity using SDSS DR17 spectroscopy. Our analysis employs a multivariate calibration that incorporates both the Eddington ratio and the rest-frame wavelength to refine the mass estimates. We obtain median DRW-based black hole masses of log ( MDRW BH / M) = 6 . 25 ±0 . 65 for NLSy1s and 7 . 07 ±0 . 67 for BLSy1s, in agreement with their respective virial mass distributions. Furthermore, we identify strong inverse trends between the variability amplitude and both optical luminosity and Fe II emission strength, consistent with a scenario where higher accretion rates suppress long-term optical variability. These findings reinforce the view that NLSy1s harbor smaller black holes and highlight the value of variability-based approaches in tracing AGN accretion properties.