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Register a new userDetermining Inclinations of Active Galactic Nuclei Via Their Narrow-Line Region Kinematics - II. Correlation With Observed Properties
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Active Galactic Nuclei (AGN) are axisymmetric systems to first order; their observed properties are likely strong functions of inclination with respect to our line of sight, yet the specific inclinations of all but a few AGN are generally unknown. By determining the inclinations and geometries of nearby Seyfert galaxies using the kinematics of their narrow-line regions (NLRs), and comparing them with observed properties, we find strong correlations between inclination and total hydrogen column density, infrared color, and H-beta full-width at half maximum (FWHM). These correlations provide evidence that the orientation of AGN with respect to our line of sight affects how we perceive them, beyond the Seyfert type dichotomy. They can also be used to constrain 3D models of AGN components such as the broad-line region and torus. Additionally, we find weak correlations between AGN luminosity and several modeled NLR parameters, which suggests that the NLR geometry and kinematics are dependent to some degree on the AGNs radiation field.
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We have analyzed HST spectroscopy of 24 nearby AGNs to investigate spatially-resolved gas kinematics in the Narrow Line Region (NLR). These observations effectively isolate the nuclear line profiles on less than 100 pc scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion sigma_* of the host galaxy, a quantity which relates with substantially less scatter to the mass of the central, supermassive black hole, and more generally characterize variations in the NLR velocity field with radius. We find that line widths measured with STIS at a range of spatial scales systematically underestimate both sigma_* and the line width measured from ground-based observations, although they do have comparably large scatter to the relation between ground-based NLR line width and sigma_*. There are no obvious trends in the residuals when compared with a range of host galaxy and nuclear properties. The widths and asymmetries of [OIII] 5007 and [SII] 6716, 6731 as a function of radius exhibit a wide range of behavior. Some of the most common phenomena are substantial width increases from the STIS to the large-scale, ground-based aperture and almost no change in line profile between the unresolved nuclear spectrum and ground-based measurements. We identify asymmetries in a surprisingly large fraction of low-ionization [SII] line profiles and several examples of substantial red asymmetries in both [OIII] and [SII]. These results underscore the complexity of the circumnuclear material that constitutes the NLR and suggest that the scatter in the NLR width and sigma_* correlation can not be substantially reduced with a simple set of empirical relations.
We present an analysis of STIS/HST optical spectra of a sample of ten Seyfert galaxies aimed at studying the structure and physical properties of the coronal-line region (CLR). The high-spatial resolution provided by STIS allowed us to resolve the CLR and obtain key information about the kinematics of the coronal-line gas, measure directly its spatial scale, and study the mechanisms that drive the high-ionisation lines. We find CLRs extending from just a few parsecs (~10 pc) up to 230 pc in radius, consistent with the bulk of the coronal lines (CLs) originating between the BLR and NLR, and extending into the NLR in the case of [FeVII] and [NeV] lines. The CL profiles strongly vary with the distance to the nucleus. We observed line splitting in the core of some of the galaxies. Line peak shifts, both red- and blue-shifts, typically reached 500 km/s, and even higher velocities (1000 km/s) in some of the galaxies. In general, CLs follow the same pattern of rotation curves as low-ionisation lines like [OIII]. From a direct comparison between the radio and the CL emission we find that neither the strength nor the kinematics of the CLs scale in any obvious and strong way with the radio jets. Moreover, the similarity of the flux distributions and kinematics of the CLs and low-ionisation lines, the low temperatures derived for the gas, and the success of photoionisation models to reproduce, within a factor of few, the observed line ratios, point towards photoionisation as the main driving mechanism of CLs.
The location of warm dust producing the Mid-infrared (MIR) emission in Type 1 Active Galactic Nuclei (AGNs) is complex and not yet fully known. We explore this problem by studying how the MIR covering factor (CF_{MIR} =L_{MIR}/L_{bol}) correlates with the fundamental parameters of AGN accretion process (such as L_{bol}, black hole mass MBH, and Eddington ratio L/LEdd) and the properties of narrow emission lines (as represented by [O III] 5007), using large data sets derived from the Sloan Digital Sky Spectroscopic Survey (SDSS) and the Wide Infrared Sky Survey (WISE). Firstly we find that the luminosity of the [O III] wing component (Lwing) correlates more tightly with the continuum luminosity (L5100) than the luminosity of the line core component (Lcore) does, which is in line with our previous conclusion that the wing component, generally blueshifted, originates from the polar outflows in the inner narrow-line region (NLR). We then find that the MIR CF shows the strongest correlation with Lwing/L_{bol} rather than with Lcore/L_{bol} or the above fundamental AGN parameters, and the correlation becomes stronger as the infrared wavelength increases. We also confirm the anti-correlations of CF_{MIR} with L_{bol} and MBH, and the lack of dependence of CF_{MIR} on the Eddington ratio. These results suggest that a large fraction of the warm dust producing MIR emission in AGNs is likely embedded in polar outflows in the NLR instead of in the torus.
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.
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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