Are Narrow-line Seyfert 1 Galaxies Powered by Low-mass Black Holes?
Suvendu Rakshit; Gayathri Viswanath; K. Ujjwal; Shivappa B. Gudennavar; C. S. Stalin; Kshama S. Kurian; Sreeja S. Kartha
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 MBH ∼ 106–108 Msun. 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 MBH. To resolve this tension of low MBH 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(MBH,AD/Msun) of 7.98 ± 0.54. For RQ-NLS1s and RQ-BLS1s
we found mean log(MBH,AD/Msun) of 8.00 ± 0.43 and 7.90 ± 0.57, respectively. While the derived MBH,AD values of
RQ-BLS1s are similar to their virial masses, for NLS1s the derived MBH,AD values are about an order of magnitude
larger than their virial estimates. Our analysis thus indicates that NLS1s have MBH similar to RQ-BLS1s and their
available virial MBH values are underestimated, influenced by their observed relatively small emission line widths.
Considering the Eddington ratio as an estimation of the accretion rate and using MBH,AD, we found the mean accretion
rate of our RQ-NLS1s, RL-NLS1s, and RQ-BLS1s as 0.06, 0.05 and 0.05, respectively. Our results, therefore, suggest that NLS1s have BH masses and accretion rates that are similar to BLS1s.
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