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Register a new userBLR size in Realistic FRADO Model: The role of shielding effect
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Mohammad-Hassan Naddaf
Publication date
2020
fields
Physics
and research's language is
English
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The effective size of Broad Line Region (BLR), so-called the BLR radius, in galaxies with active galactic nuclei (AGN) scales with the source luminosity. Therefore by determining this location either observationally through reverberation mapping or theoretically, one can use AGNs as an interesting laboratory to test cosmological models. In this article we focus on the theoretical side of BLR based on the Failed Radiatively Accelerated Dusty Outflow (FRADO) model. By simulating the dynamics of matter in BLR through a realistic model of radiation of accretion disk (AD) including the shielding effect, as well as incorporating the proper values of dust opacities, we investigate how the radial extension and geometrical height of the BLR depends on the Eddington ratio [and blackhole mass], and modeling of shielding effect. We show that assuming a range of Eddington ratios and shielding we are able to explain the measured time-delays in a sample of reverberation-measured AGNs.
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The dynamics of the Broad Line Region (BLR) in Active galaxies is an open question, direct observational constraints suggest a predominantly Keplerian motion, with possible traces of inflow or outflow. In this paper we study in detail the physically motivated BLR model of (Czerny & Hryniewicz, 2011) based on the radiation pressure acting on dust at the surface layers of accretion disk (AD). We consider here a non-hydrodynamical approach to the dynamics of the dusty cloud under the influence of radiation coming from the entire AD. We use here the realistic description of the dust opacity, and we introduce two simple geometrical models of the local shielding of the dusty cloud. We show that the radiation pressure acting on dusty clouds is strong enough to lead to dynamical outflow from the AD surface, so the BLR has a dynamical character of (mostly failed) outflow. The dynamics strongly depend on the Eddington ratio of the source. Large Eddington ratio sources show a complex velocity field and large vertical velocities with respect to the AD surface, while for lower Eddington ratio sources vertical velocities are small and most of the emission originates close to the AD surface. Cloud dynamics thus determines the 3-D geometry of the BLR.
In Failed Radiatively Accelerated Dusty Outflow (FRADO) model which provides the source of material above the accretion disk (AD) as an option to explain the formation mechanism of Broad Line Region (BLR) in AGNs, the BLR inner radius ($rm{BLR}_{in}$ hereafter) is set by the condition that the dust evaporates immediately upon departure from the AD surface. On the other hand, the location of BLR clouds obtained observationaly via reverberation mapping shows some scaling with the source luminosity, so-called RL relation. We assume $rm{BLR}_{in}$ to be the location of BLR clouds, then using a realistic expression for the radiation pressure of an AD, and having included the proper values of dust opacity, and shielding effect as well, we report our numerical results on calculation of $rm{BLR}_{in}$ based on FRADO model. We investigate how it scales with monochromatic luminosity at 5100 angstrom for a grid of blackhole masses and Eddington ratios to compare along with the FRADO analytically predicted RL directly to observational data.
For a compiled sample of 120 reverberation-mapped AGNs, the bivariate correlations of the broad-line regions (BLRs) size ($R_{rm BLR}$) with the continuum luminosity at 5100 AA ($L_{5100}$) and the dimensionless accretion rates ($dot{mathscr{M}}$) are investigated. Using our recently calibrated virial factor $f$, and the velocity tracer from the H$beta$ Full-width at half-maximum (FWHM(H$beta$)) or the line dispersion ($sigma_{rm Hbeta}$) measured in the mean spectra, three kinds of SMBH masses and $dot{mathscr{M}}$ are calculated. An extended RL relation including $dot{mathscr{M}}$ is found to be stronger than the canonical $R_{rm BLR}({rm Hbeta}) - L_{rm 5100}$ relation, showing smaller scatters. The observational parameters, $R_{rm Fe}$ (the ratio of optical Fe II to H$beta$ line flux) and the line profile parameter $D_{rm Hbeta}$ ($D_{rm Hbeta}=rm FWHM(Hbeta)/sigma_{rm Hbeta}$), have relations with three kinds of $dot{mathscr{M}}$. Using $R_{rm Fe}$ and $D_{rm Hbeta}$ to substitute $dot{mathscr{M}}$, extended empirical $R_{rm BLR}({rm Hbeta}) - L_{rm 5100}$ relations are presented. $R_{rm Fe}$ is a better fix for the $R_{rm BLR}({rm Hbeta}) - L_{rm 5100}$ offset than the H$beta$ shape $D_{rm Hbeta}$. The extended empirical $R_{rm BLR}({rm Hbeta}) - L_{rm 5100}$ relation including $R_{rm Fe}$ can be used to calculate $R_{rm BLR}$, and thus the single-epoch SMBH mass $M_{rm BH}$. Our measured accretion rate dependence is not consistent with the simple model of the accretion disk instability leading the BLRs formation. The BLR may instead form from the inner edge of the torus, or from some other means in which BLR size is positively correlated with accretion rate and the SMBH mass.
Active galactic nuclei (AGNs) show a correlation between the size of the broad line region (BLR) and the monochromatic continuum luminosity at 5100 AA, allowing black hole mass estimation based on single-epoch spectra. However, the validity of the correlation is yet to be clearly tested for high-luminosity AGNs. We present the first reverberation-mapping results of the Seoul National University AGN monitoring program (SAMP), which is designed to focus on luminous AGNs for probing the high end of the size-luminosity relation. We report time lag measurements of two AGNs, namely, 2MASS J10261389+5237510 and SDSS J161911.24+501109.2, using the light curves obtained over a $sim$1000 day period with an average cadence of $sim$10 and $sim$20 days, respectively for photometry and spectroscopy monitoring. Based on a cross-correlation analysis and H$beta$ line width measurements, we determine the H$beta$ lag as $41.8^{+4.9}_{-6.0}$ and $52.6^{+17.6}_{-14.7}$ days in the observed-frame, and black hole mass as $3.65^{+0.49}_{-0.57} times 10^7 M_{odot}$ and $23.02^{+7.81}_{-6.56} times 10^7 M_{odot}$, respectively for 2MASS J1026 and SDSS J1619.
As self-gravitating systems, dense star clusters exhibit a natural diffusion of energy from their innermost to outermost regions, which leads to a slow and steady contraction of the core until it ultimately collapses under gravity. However, in spite of the natural tendency toward so-called core collapse, the globular clusters (GCs) in the Milky Way exhibit a well-observed bimodal distribution in core radii separating the core-collapsed and non-core-collapsed clusters. This suggests an internal energy source is at work, delaying the onset of core collapse in many clusters. Primordial binary stars have been thought for a long time to provide this energy source, but recent analyses have cast doubt upon the corresponding binary-burning mechanism as a viable explanation. Over the past decade, a large amount of both observational and theoretical work has suggested that many stellar-mass black holes (BHs) are retained in typical clusters today and that they play a dynamically-significant role in these clusters throughout their entire lifetimes. Here we review our latest understanding of the formation and evolution of BH populations in GCs and demonstrate that, through their dynamical interaction with their host cluster, BHs can naturally explain the distinction between core-collapsed and non-core-collapsed clusters through a process we call black hole burning.
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