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Register a new userInterpretation of Departure from the Broad Line Region Scaling in Active Galactic Nuclei
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Most results of the reverberation monitoring of active galaxies showed a universal scaling of the time delay of the Hbeta emission region with the monochromatic flux at 5100 A, with very small dipersion. Such a scaling favored the dust-based formation mechanism of the Broad Line Region (BLR). Recent reverberation measurements showed that actually a significant fraction of objects exhibits horter lags than the previously found scaling. Here we demonstrate that these shorter lags can be explained by the old concept of scaling of the BLR size with the ionization parameter. Assuming a universal value of this parameter and universal value of the cloud density reproduces the distribution of observational points in the time delay vs. monochromatic flux plane, provided that a range of black hole spins is allowed. However, a confirmation of the new measurements for low/moderate Eddington ratio sources is strongly needed before the dust-based origin of the BLR can be excluded.
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Apart from viewing-dependent obscuration, intrinsic broad-line emission from active galactic nuclei (AGNs) follows an evolutionary sequence: Type $1 to 1.2/1.5 to 1.8/1.9 to 2$ as the accretion rate onto the central black hole is decreasing. This spectral evolution is controlled, at least in part, by the parameter $L_{rm bol}/M^{2/3}$, where $L_{rm bol}$ is the AGN bolometric luminosity and $M$ is the black hole mass. Both this dependence and the double-peaked profiles that emerge along the sequence arise naturally in the disk-wind scenario for the AGN broad-line region.
Broad emission lines in active galactic nuclei (AGNs) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. The shape of the broad-line profile, described by ${cal D}_{_{rm Hbeta}}={rm FWHM}/sigma_{_{rm Hbeta}}$, the ratio of full width at half maximum to the dispersion of broad H$beta$, reflects the dynamics of the broad-line region (BLR) and correlates with the dimensionless accretion rate ($dot{mathscr{M}}$) or Eddington ratio ($L_{rm bol}/L_{rm Edd}$). At the same time, $dot{mathscr{M}}$ and $L_{rm bol}/L_{rm Edd}$ correlate with ${cal R}_{rm Fe}$, the ratio of optical Fe II to H$beta$ line flux emission. Assembling all AGNs with reverberation mapping measurements of broad H$beta$, both from the literature and from new observations reported here, we find a strong bivariate correlation of the form $log(dot{mathscr{M}},L_{rm bol}/L_{rm Edd})=alpha+beta{cal D}_{_{rm Hbeta}}+gamma{cal R}_{rm Fe},$ where $alpha=(2.47,0.31)$, $beta=-(1.59,0.82)$ and $gamma=(1.34,0.80)$. We refer to this as the fundamental plane of the BLR. We apply the plane to a sample of $z < 0.8$ quasars to demonstrate the prevalence of super-Eddington accreting AGNs are quite common at low redshifts.
Supermassive black holes in active galactic nuclei (AGNs) undergo a wide range of accretion rates, which lead to diversity of appearance. We consider the effects of anisotropic radiation from accretion disks on the broad-line region (BLR), from the Shakura-Sunyaev regime to slim disks with super-Eddington accretion rates. The geometrically thick funnel of the inner region of slim disks produces strong self-shadowing effects that lead to very strong anisotropy of the radiation field. We demonstrate that the degree of anisotropy of the radiation fields grows with increasing accretion rate. As a result of this anisotropy, BLR clouds receive different spectral energy distributions depending on their location relative to the disk, resulting in diverse observational appearance of the BLR. We show that the self-shadowing of the inner parts of the disk naturally produces two dynamically distinct regions of the BLR, depending on accretion rate. These two regions manifest themselves as kinematically distinct components of the broad H$beta$ line profile with different line widths and fluxes, which jointly account for the Lorentzian profile generally observed in narrow-line Seyfert 1 galaxies. In the time domain, these two components are expected reverberate with different time lags with respect to the varying ionizing continuum, depending on the accretion rate and the viewing angle of the observer. The diverse appearance of the BLR due to the anisotropic ionizing energy source can be tested by reverberation mapping of H$beta$ and other broad emission lines (e.g., feii), providing a new tool to diagnose the structure and dynamics of the BLR. Other observational consequences of our model are also explored.
This paper reports results of the third-year campaign of monitoring super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs) between 2014-2015. Ten new targets were selected from quasar sample of Sloan Digital Sky Survey (SDSS), which are generally more luminous than the SEAMBH candidates in last two years. H$beta$ lags ($tau_{_{rm Hbeta}}$) in five of the 10 quasars have been successfully measured in this monitoring season. We find that the lags are generally shorter, by large factors, than those of objects with same optical luminosity, in light of the well-known $R_{_{rm Hbeta}}-L_{5100}$ relation. The five quasars have dimensionless accretion rates of $dot{mathscr{M}}=10-10^3$. Combining measurements of the previous SEAMBHs, we find that the reduction of H$beta$ lags tightly depends on accretion rates, $tau_{_{rm Hbeta}}/tau_{_{R-L}}proptodot{mathscr{M}}^{-0.42}$, where $tau_{_{R-L}}$ is the H$beta$ lag from the normal $R_{_{rm Hbeta}}-L_{5100}$ relation. Fitting 63 mapped AGNs, we present a new scaling relation for the broad-line region: $R_{_{rm Hbeta}}=alpha_1ell_{44}^{beta_1},minleft[1,left(dot{mathscr{M}}/dot{mathscr{M}}_cright)^{-gamma_1}right]$, where $ell_{44}=L_{5100}/10^{44},rm erg~s^{-1}$ is 5100 AA continuum luminosity, and coefficients of $alpha_1=(29.6_{-2.8}^{+2.7})$ lt-d, $beta_1=0.56_{-0.03}^{+0.03}$, $gamma_1=0.52_{-0.16}^{+0.33}$ and $dot{mathscr{M}}_c=11.19_{-6.22}^{+2.29}$. This relation is applicable to AGNs over a wide range of accretion rates, from $10^{-3}$ to $10^3$. Implications of this new relation are briefly discussed.
It has been recently proposed that the broad line region in active galactic nuclei originates from dusty clouds driven from the accretion disk by radiation pressure, at a distance from the black hole where the disk is cooler than the dust sublimation temperature. We test this scenario by checking the consistency of independent broad line region and accretion disk reverberation measurements, for a sample of 11 well studied active galactic nuclei. We show that independent disk and broad line region reverberation mapping measurements are compatible with a universal disk temperature at the H{beta} radius of T[R(H{beta})]=1670(231) K which is close to typical dust sublimation temperatures.
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