Are narrow-line seyfert 1 galaxies powered by low-mass black holes?

Abstract

Are Narrow-line Seyfert 1 Galaxies Powered by Low-mass Black Holes? Gayathri Viswanath 1 , C. S. Stalin 2 , Suvendu Rakshit 3 , Kshama S. Kurian 2 , K. Ujjwal 1 , Shivappa B. Gudennavar 1 , and Sreeja S. Kartha 1 1 Department of Physics and Electronics, CHRIST ( Deemed to be University ) , Bengaluru, Karnataka 560029, India 2 Indian Institute of Astrophysics, Block II, Koramangala, Bengaluru, Karnataka 560034, India 3 Finnish Centre for Astronomy with ESO ( FINCA ) , University of Turku, Quantum, Vesilinnantie 5, FI-20014, Finland; suvenduat@gmail.com Received 2019 April 3; revised 2019 June 21; accepted 2019 July 1; published 2019 August 13 Abstract 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

∼  10 6 – 10 8 M e . However, the broadband spectral energy distribution of the γ -ray-emitting NLS1s are found to be similar to fl at-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 fi tted 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 (

MM BH AD ) of 7.98

±

0.54. For RQ-NLS1s and RQ-BLS1s we found mean log

MM BH AD ) 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, in fl uenced 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.