Reverberation mapping of narrow-line Seyfert 1 galaxy I Zwicky 1: black hole mass

Abstract

We report results of the first reverberation mapping campaign of I Zwicky 1 during $2014$-$2016$, which showed unambiguous reverberations of the broad H${\hat{I}}^2$ line emission to the varying optical continuum. From analysis using several methods, we obtain a reverberation lag of $\ddot{I}{„}_{\mathrm{H}{\hat{\mathrm{I}}}^2}=37.2_{-4.9}^{+4.5}$ days. Taking a virial factor of $f_{{}_{\mathrm{BLR}}}=1$, we find a black hole mass of $M_{\bullet }=9.30_{-1.38}^{+1.26}\times 10^6{M}_{\odot }$ from the mean spectra. The accretion rate is estimated to be $203.9_{-65.8}^{+61.0}{L}_{\mathrm{Edd}}{c}^{-2}$, suggesting a super-Eddington accretor, where $L_{\mathrm{Edd}}$ is the Eddington luminosity and $c$ is the speed of light. By decomposing {\it Hubble Space Telescope} images, we find that the stellar mass of the bulge of its host galaxy is $\log (M_{\mathrm{bulge}}/M_{\odot })=10.92\pm 0.07$. This leads to a black hole to bulge mass ratio of $\sim 10^{-4}$, 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 $R_{\mathrm{BLR}}\propto L_{5100}^{1/2}$ relation.

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