Off-Axis Energy Variability of AGNs: a New Paradigm for Broad-Line- and Continuum-Emitting Regions (original) (raw)
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Off-Axis Variability of AGNs: a New Paradigm for Broad Lines and Continuum Emitting Regions
The general picture of how thermal AGNs work has become clearer in recent years but major observational puzzles threaten to undermine this picture. These puzzles include AGNs with extremely asymmetric emission line profiles, inconsistent multi-wavelength variability, rapid apparent changes in the sizes of emitting regions and in the direction of gas flow, a curious insensitivity of gas in some narrow velocity ranges to changes in the ionizing continuum, and differing dependences of polarization on gas velocity. It is proposed that all these puzzles can readily be explained by off-axis variability.
Off-Axis Variability of AGNs: a New Paradigm for Broad-Line and Continuum-Emitting Regions
The general picture of how thermal AGNs work has become clearer in recent years but major observational puzzles threaten to undermine this picture. These puzzles include AGNs with extremely asymmetric emission line profiles, inconsistent multi-wavelength variability, rapid apparent changes in the sizes of emitting regions and in the direction of gas flow, a curious insensitivity of gas in some narrow velocity ranges to changes in the ionizing continuum, and differing dependences of polarization on gas velocity. It is proposed that all these puzzles can readily be explained by off-axis variability.
2011
The general picture of how thermal AGNs work has become clearer in recent years but major observational puzzles threaten to undermine this picture. These puzzles include AGNs with extremely asymmetric emission line profiles, inconsistent multi-wavelength variability, rapid apparent changes in the sizes of emitting regions and in the direction of gas flow, a curious insensitivity of gas in some narrow velocity ranges to changes in the ionizing continuum, and differing dependences of polarization on gas velocity. It is proposed that all these puzzles can readily be explained by off-axis variability.
The link between broad emission line fluctuations and non-thermal emission from the inner AGN jet
Proceedings of the International Astronomical Union, 2014
AGN reverberate when the broad emission lines respond to changes of the ionizing thermal continuum emission. Reverberation measurements have been commonly used to estimate the size of the broad-line region (BLR) and the mass of the central black hole. However, reverberation mapping studies have been mostly performed on radio-quiet sources where the contribution of the jet can be neglected. In radio-loud AGN, jets and outflows may affect substantially the relation observed between the ionizing continuum and the line emission. To investigate this relation, we have conducted a series of multi-wavelength studies of radio-loud AGN, combining optical spectral line monitoring with regular VLBI observations. Our results suggest that at least a fraction of the broad-line emitting material can be located in a sub-relativistic outflow ionized by non-thermal continuum emission generated in the jet at large distances (> 1 pc) from the central engine of AGN. This finding may have a strong impa...
Long-term variability of the Broad Emission Line profiles in AGN
New Astronomy Reviews, 2009
Results of a long-term monitoring (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 Hα and Hβ 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.
Intermediate-line Emission in AGNs: The Effect of Prescription of the Gas Density
The Astrophysical Journal, 2018
The requirement of an intermediate-line component in the recently observed spectra of several active galactic nuclei (AGNs) points to the possible existence of a physically separate region between the broad-line region (BLR) and narrow-line region (NLR). In this paper we explore the emission from the intermediate-line region (ILR) by using photoionization simulations of the gas clouds distributed radially from the center of the AGN. The gas clouds span distances typical for the BLR, ILR, and NLR, and the appearance of dust at the sublimation radius is fully taken into account in our model. The structure of a single cloud is calculated under the assumption of constant pressure. We show that the slope of the power-law radial profile of the cloud density does not affect the existence of the ILR in major types of AGNs. We found that the low-ionization iron line, Fe II, appears to be highly sensitive to the presence of dust and therefore becomes a potential tracer of dust content in line-emitting regions. We show that the use of a disk-like cloud density profile computed for the upper part of the atmosphere of the accretion disk reproduces the observed properties of the line emissivities. In particular, the distance of the Hβ line inferred from our model agrees with that obtained from reverberation mapping studies in the Sy1 galaxy NGC5548.
Discovery of 21 New Changing-look AGNs in the Northern Sky
The Astrophysical Journal, 2018
The rare case of changing-look (CL) AGNs, with the appearance or disappearance of broad Balmer emission lines within a few years, challenges our understanding of the AGN unified model. We present a sample of 21 new CL AGNs at 0.08 < z < 0.58, which doubles the number of such objects known to date. These new CL AGNs were discovered by several ways, from (1) repeat spectra in the SDSS, (2) repeat spectra in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and SDSS, and (3) photometric variability and new spectroscopic observations. We use the photometric data from surveys, including the SDSS imaging survey, the Pan-STARRS1, the DESI Legacy imaging survey, the Wide-field Infrared Survey Explorer (WISE), the Catalina Real-time Transient Survey, and the Palomar Transient Factory. The estimated upper limits of transition timescale of the CL AGNs in this sample spans from 0.9 to 13 years in the rest frame. The continuum flux in the optical and mid-infrared becomes brighter when the CL AGNs turn on, or vice versa. Variations of more than 0.2 mag in W 1 band were detected in 15 CL AGNs during the transition. The optical and mid-infrared variability is not consistent with the scenario of variable obscuration in 10 CL AGNs at more than 3σ confidence level. We confirm a bluer-when-brighter trend in the optical. However, the mid-infrared WISE colors W 1 − W 2 become redder when the objects become brighter in the W 1 band, possibly due to a stronger hot dust contribution in the W 2 band when the AGN activity becomes stronger. The physical mechanism of type transition is important for understanding the evolution of AGNs.
2014
The anti-correlations between the equivalent widths of emission lines and the continuum luminosity in AGNs, known as the Baldwin effect are well established for broad lines, but are less well studied for narrow lines. In this paper we explore the Baldwin effect of narrow emission lines over a wide range of ionization levels and critical densities using a large sample of broad-line, radio-quiet AGNs taken from Sloan Digital Sky Survey (SDSS) Data Release 4. These type1 AGNs span three orders of magnitude in continuum luminosity. We show that most narrow lines show a similar Baldwin effect slope of about-0.2 while the significant deviations of the slopes for [N II] λ6583, [O II] λ3727, [Ne V] λ3425 , and the narrow component of Hα can be explained by the influence of metallicity, star-formation contamination and possibly by difference in the shape of the UV-optical continuum. The slopes do not show any correlation with either the ionization potential or the critical density. We show that a combination of 50% variations in continuum near 5100Å and a log-normal distribution of observed luminosity can naturally reproduce a constant Baldwin effect slope of-0.2 for all narrow lines. The variations of the continuum could be due to variability, intrinsic anisotropic emission, or an inclination effect.
The Astrophysical Journal, 2006
Deep X-ray surveys by Chandra and XMM-Newton have resolved about 80% of the 2Y10 keV cosmic extragalactic X-ray background (CXRB) into point sources, the majority of which are obscured AGNs. The obscuration might be connected to processes within the host galaxy, possibly the star formation rate. Here we use the results of CXRB synthesis calculations as input to detailed CLOUDY simulations in order to predict the evolution of AGN properties at several mid-IR wavelengths. Computations were performed for three different evolutions of the AGN type 2 /type 1 ratio between z ¼ 0 and 1, where the ratio increased as (1 þ z) 0:9 , as (1 þ z) 0:3 , and with one model having no redshift evolution. Models were calculated with the inner radius of the absorbing gas and dust at 1 or at 10 pc. Comparing the results of the calculations to combined X-ray and Spitzer data of AGNs show that the predicted spectral energy distributions are a good description of average AGNs found in the deep surveys. The existing data indicate that the mid-IR emission from an average AGN is best described by models in which the attenuating material is 10pcfromthecentralengine.WepresenttheexpectedSpitzercumulativenumbercountdistributionsandtheevolutionofthetotalAGN(type1+type2)luminosityfunction(LF)betweenz¼0and1atrestframe8and30mforthethreeevolutionaryscenarios.Themid−IRAGNLFwillbeanexcellenttooltomeasuretheevolutionofthecoveringfactorofthegasanddustfromz10 pc from the central engine. We present the expected Spitzer cumulative number count distributions and the evolution of the total AGN (type 1+type 2) luminosity function (LF ) between z ¼ 0 and 1 at rest frame 8 and 30 m for the three evolutionary scenarios. The mid-IR AGN LF will be an excellent tool to measure the evolution of the covering factor of the gas and dust from z 10pcfromthecentralengine.WepresenttheexpectedSpitzercumulativenumbercountdistributionsandtheevolutionofthetotalAGN(type1+type2)luminosityfunction(LF)betweenz¼0and1atrestframe8and30mforthethreeevolutionaryscenarios.Themid−IRAGNLFwillbeanexcellenttooltomeasuretheevolutionofthecoveringfactorofthegasanddustfromz0 to 1.
Radio-optical study of double-peaked AGNs
Proceedings of From Planets to Dark Energy: the Modern Radio Universe — PoS(MRU)
We aim to test the model proposed to explain the correlation between the flux density at 15 GHz of a stationary component in the parsec-scale jet and the optical continuum emission in the radio galaxy 3C 390.3. In the model, the double-peaked emission from 3C 390.3 is likely to be generated both near the disk and in a rotating subrelativistic outflow surrounding the jet, due to ionization of the outflow by the beamed continuum emission from the jet. This scenario is chosen since broad-emission lines are observed to vary following changes in the inner radio jet. For recent epochs we have imaged and modelled the radio emission of the inner jet of 3C 390.3, which was observed with very long baseline interferometry at 15 GHz, 22 GHz and 43 GHz, to image the inner part of the parsec-scale jet, locate the exact region where the bulk of the continuum luminosity is generated and search for the mechanism that drives the double-peaked profile emission. We present the preliminary results of testing the model using data from 11 years of active monitoring of 3C 390.3.