2019ApJ...881L..24V

Narrow-line Seyfert 1 galaxies (NLS1s) are believed to be powered by the accretion of matter onto low-mass black holes (BHs) in spiral host galaxies with BH masses M_BH ∼ 10⁶-10⁸ M_☉. However, the broadband spectral energy distribution of the γ-ray-emitting NLS1s are found to be similar to flat-spectrum radio quasars. This challenges our current notion of NLS1s having low M_BH. To resolve this tension of low M_BH values in NLS1s, we fitted the observed optical spectrum of a sample of radio-loud NLS1s (RL-NLS1s), radio-quiet NLS1s (RQ-NLS1s), and radio-quiet broad-line Seyfert 1 galaxies (RQ-BLS1s) of ∼500 each with the standard Shakura-Sunyaev accretion disk (AD) model. For RL-NLS1s we found a mean log(M_BH^AD/M_☉) of 7.98 ± 0.54. For RQ-NLS1s and RQ-BLS1s we found mean log(M_BH^AD/M_☉) of 8.00 ± 0.43 and 7.90 ± 0.57, respectively. While the derived M_BH^AD values of RQ-BLS1s are similar to their virial masses, for NLS1s the derived M_BH^AD values are about an order of magnitude larger than their virial estimates. Our analysis thus indicates that NLS1s have M_BH similar to RQ-BLS1s and their available virial M_BH values are underestimated, influenced by their observed relatively small emission line widths. Considering Eddington ratio as an estimation of the accretion rate and using M_BH^AD, we found the mean accretion rate of our RQ-NLS1s, RL-NLS1s, and RQ-BLS1s as 0.06_–0.05^+0.16, 0.05_–0.04^+0.18 and 0.05_–0.04^+0.15, respectively. Our results therefore suggest that NLS1s have BH masses and accretion rates that are similar to BLS1s.