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Register a new userBroad Emission Line Regions in AGN: the Link with the Accretion Power
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We present a model which relates the width of the Broad Emission Lines of AGN to the Keplerian velocity of an accretion disk at a critical distance from the central black hole. This critical distance falls in a region bounded on the inward side by the transition radius between the radiation pressure and the gas pressure dominated region of the accretion disk and on the outward side by the maximum radius below which a stabilizing, radially accreting and vertically outflowing corona exists. We show that in the framework of this picture the observed range of H$beta$ FWHM from Broad Line to Narrow Line type 1 AGN is well reproduced as a function of the accretion rate. This interval of velocities is the only permitted range and goes from $sim 20,000$ km s$^{-1}$ for sub-Eddington accretion rates, to $sim 1,000$ km s$^{-1}$ for Eddington accretion rates.
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The masses of supermassive black holes in active galactic nuclei (AGN) can be derived spectroscopically via virial mass estimators based on selected broad optical/ultraviolet emission lines. These estimates commonly use the line width as a proxy for the gas speed and the monochromatic continuum luminosity as a proxy for the radius of the broad line region. However, if the size of the broad line region scales with bolometric rather than monochromatic AGN luminosity, mass estimates based on different emission lines will show a systematic discrepancy which is a function of the color of the AGN continuum. This has actually been observed in mass estimates based on H-alpha / H-beta and C IV lines, indicating that AGN broad line regions indeed scale with bolometric luminosity. Given that this effect seems to have been overlooked as yet, currently used single-epoch mass estimates are likely to be biased.
The Broad Emission Lines (BELs) in spectra of type 1 Active Galactic Nuclei (AGN) can be very complex, indicating a complex Broad Line Region (BLR) geometry. According to the standard unification model one can expect an accretion disk around a supermassive black hole in all AGN. Therefore, a disk geometry is expected in the BLR. However, a small fraction of BELs show double-peaked profiles which indicate the disk geometry. Here, we discuss a two-component model, assuming an emission from the accretion disk and one additional emission from surrounding region. We compared the modeled BELs with observed ones (mostly broad H$alpha$ and H$beta$ profiles) finding that the model can well describe single-peaked and double-peaked observed broad line profiles.
Using a large sample of 90 Seyfert 2 galaxies (Sy2s) with spectropolarimetric observations, we tested the suggestion that the presence of hidden broad-line regions (HBLRs) in Sy2s is dependent upon the Eddington ratio. The stellar velocity dispersion and the extinction-corrected $OIII$ luminosity are used to derive the mass of central super-massive black holes and the Eddington ratio. We found that: (1) below the Eddington ratio threshold of $10^{-1.37}$, all but one object belong to non-HBLRs Sy2s; while at higher Eddington ratio, there is no obvious discrimination in the Eddington ratio and black hole mass distributions for Sy2s with and without HBLRs; (2) nearly all low-luminosity Sy2s (e.g., $LOIII < 10^{41} ergs$) do not show HBLRs regardless of the column density of neutral hydrogen ($N_{rm H}$); (3) for high-luminosity Sy2s, the possibility to detect HBLRs Sy2s is almost the same as that of non-HBLRs Sy2s; (4) when considering only Compton-thin Sy2s with higher $OIII$ luminosity ($>10^{41} ergs$), we find a very high detectability of HBLRs ,$sim$ 85%. These results suggested that AGN luminosity plays a major role in not detecting HBLRs in low-luminosity Sy2s, while for high-luminosity Sy2s, the detectability of HBLRs depends not only upon the AGN activity, but also upon the torus obscuration.
Results of a long-term monitoring ($gtrsim 10$ years) of the broad line and continuum fluxes of three Active Galactic Nuclei (AGN), 3C 390.3, NGC 4151, and NGC 5548, are presented. We analyze the H$alpha$ and H$beta$ profile variations during the monitoring period and study different details (as bumps, absorption bands) which can indicate structural changes in the Broad Line Region (BLR). The BLR dimensions are estimated using the time lags between the continuum and the broad lines flux variations. We find that in the case of 3C 390.3 and NGC 5548 a disk geometry can explain both the broad line profiles and their flux variations, while the BLR of NGC 4151 seems more complex and is probably composed of two or three kinematically different regions.
We measured the metallicity Z in the broad emission line regions (BELRs) of 43 SDSS quasars with the strongest N IV] and N III] emission lines. These N-Loud QSOs have unusually low black hole masses. We used the intensity ratio of N lines to collisionally-excited emission lines of other heavy elements to find metallicities in their BELR regions. We found that 7 of the 8 line-intensity ratios that we employed give roughly consistent metallicities as measured, but that for each individual QSO their differences from the mean of all metallicity measurements depends on the ionization potential of the ions that form the emission lines. After correcting for this effect, the different line-intensity ratios give metallicities that generally agree to within the 0.24 dex uncertainty in the measurements of the line-intensity ratios. The metallicities are very high, with mean log Z for the whole sample of 5.5 Z_sun and a maximum of 18 Z_sun. Our results argue against the possibility that the strong N lines represent an overabundance only of N but not of all heavy elements. They are compatible with either (1) the BELR gas has been chemically enriched by the general stellar population in the central bulge of the host galaxy but the Locally Optimally-emitting Cloud model used in the analysis needs some fine tuning, or (2) that instead this gas has been enriched by intense star formation on the very local scale of the active nucleus that has resulted in an abundance gradient within the BELR.
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