Reverberation Mapping of the Narrow-line Seyfert 1 Galaxy I Zwicky 1: Black Hole Mass

We report results of the first reverberation mapping campaign of I Zwicky 1 during 2014-2016, which showed unambiguous reverberations of the broad H beta line emission in the varying optical continuum. From analysis using several methods, we obtain a reverberation lag of tau(H beta) = 37.2(-4.9)(+4.5) days. Taking a virial factor of f(BLR) = 1, we find a black hole mass of M. = 9.30(-1.38)(+1.26) x 10(6)M(circle dot) from the mean spectra. The accretion rate is estimated to be 203.9(-65.8)(+61.0) L-Edd c(-2), suggesting a super-Eddington accretor, where L-Edd is the Eddington luminosity and c is the speed of light. By decomposing Hubble Space Telescope images, we find that the stellar mass of the bulge of its host galaxy is log(M-bulge/M-circle dot) = 10.92 +/- 0.07. This leads to a black hole to bulge mass ratio of similar to 10(-4), which is significantly smaller than that of classical bulges and elliptical galaxies. After subtracting the host contamination from the observed luminosity, we find that I Zw 1 follows the empirical R-BLR proportional to L-5100(1/2) relation.