Modeling Grain Rotational Disruption by Radiative Torques and Extinction of Active Galactic Nuclei

Abstract Extinction curves observed toward individual Active Galactic Nuclei (AGN) usually show a steep rise toward far-ultraviolet (FUV) wavelengths and can be described by the Small Magellanic Cloud (SMC)-like dust model. This feature suggests the dominance of small dust grains of size a ≤ 0.1 μm in the local environment of AGN, but the origin of such small grains is unclear. In this paper, we aim to explain this observed feature by applying the RAdiative Torque Disruption (RATD) to model the extinction of AGN radiation from FUV to mid-infrared (MIR) wavelengths. We find that in the intense radiation field of AGN, large composite grains of size a ≥ 0.1 μm are significantly disrupted to smaller sizes by RATD up to d RATD > 100 pc in the polar direction and d RATD ∼ 10 pc in the torus region. Consequently, optical–MIR extinction decreases, whereas FUV-near-ultraviolet extinction increases, producing a steep far-UV rise extinction curve. The resulting total-to-selective visual extinction ratio thus significantly drops to R V < 3.1 with decreasing distances to AGN center due to the enhancement of small grains. The dependence of R V with the efficiency of RATD will help us to study the dust properties in the AGN environment via photometric observations. In addition, we suggest that the combination of the strength between RATD and other dust destruction mechanisms that are responsible for destroying very small grains of a ≤ 0.05 μm is the key for explaining the dichotomy observed “SMC” and “gray” extinction curve toward many AGN.

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THE EFFECTS OF THE LOCAL ENVIRONMENT ON ACTIVE GALACTIC NUCLEI

The Astrophysical Journal ◽

10.1088/0004-637x/788/2/140 ◽

2014 ◽

Vol 788 (2) ◽

pp. 140 ◽

Cited By ~ 13

Author(s):

L. H. Manzer ◽

M. M. De Robertis

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Local Environment

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On the Optical-to-silicate Extinction Ratio as a Probe of the Dust Size in Active Galactic Nuclei

The Astrophysical Journal ◽

10.3847/1538-4357/aa6ba4 ◽

2017 ◽

Vol 840 (1) ◽

pp. 27 ◽

Cited By ~ 9

Author(s):

Zhenzhen Shao ◽

B. W. Jiang ◽

Aigen Li

Keyword(s):

Active Galactic Nuclei ◽

Extinction Ratio ◽

Galactic Nuclei

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Host galaxy properties and environment of obscured and unobscured X-ray selected active galactic nuclei in the COSMOS survey

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa723 ◽

2020 ◽

Vol 494 (1) ◽

pp. 1189-1202 ◽

Cited By ~ 1

Author(s):

C Bornancini ◽

D García Lambas

Keyword(s):

Active Galactic Nuclei ◽

Formation Rate ◽

Control Sample ◽

Galactic Nuclei ◽

Local Environment ◽

Spectroscopic Properties ◽

Stellar Mass ◽

Host Galaxy ◽

X Ray ◽

Star Forming

ABSTRACT We analyse different photometric and spectroscopic properties of active galactic nuclei (AGNs) and quasars (QSOs) selected by their mid-IR power-law and X-ray emission from the COSMOS survey. We use a set of star-forming galaxies as a control sample to compare with the results. We have considered samples of obscured (HR > −0.2) and unobscured (HR < −0.2) sources including AGNs with LX < 1044 erg s−1, as well as QSOs (LX > 1044 erg s−1) with 1.4 ≤ z ≤ 2.5. We also study the typical environment of these samples, by assessing neighbouring galaxy number density and neighbour properties such as colour, stellar mass, and star formation rate. We find that the UV/optical and mid-infrared colour distribution of the different AGN types differ significantly. Also, we obtain most of AGNs and QSOs to be more compact when compared to the sample of SF galaxies. In general we find that the stellar mass distribution of the different AGN sample are similar, obtaining only a difference of $\Delta \overline{\mathrm{log}M}=0.3$ dex (M⊙) between unobscured and obscured QSOs. Obscured and unobscured AGNs and QSOs reside in different local environment at small (rp < 100 kpc) scales. Our results support previous findings where AGN type correlates with environment. These differences and those found in AGN host properties cast out the simplest unified model in which obscuration is purely an orientation effect.

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Reddening in the Narrow-Line Region of Active Galactic Nuclei

Symposium - International Astronomical Union ◽

10.1017/s0074180900141245 ◽

1989 ◽

Vol 134 ◽

pp. 329-330

Author(s):

I.M. Yancoulova ◽

Z.I. Tsvetanov

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Narrow Line ◽

Line Region ◽

Narrow Line Region ◽

Upper Level ◽

Far Ultraviolet

The best indicators of the reddening in the narrow-line regions of AGN are ratios of pairs of forbidden lines arising from a common upper level. The ratios of [SII] λ4072/λ10320 and [OII] λ7325/λ2470 are good examples, but they include lines in the far ultraviolet and infrared regions which are difficult to observe.

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Environments of dwarf galaxies with optical AGN characteristics

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1719 ◽

2020 ◽

Vol 496 (3) ◽

pp. 2577-2590 ◽

Cited By ~ 1

Author(s):

Mikkel T Kristensen ◽

Kevin Pimbblet ◽

Samantha Penny

Keyword(s):

Emission Line ◽

Active Galactic Nuclei ◽

Dwarf Galaxies ◽

Galactic Nuclei ◽

Local Environment ◽

Selection Method ◽

Estimation Methods ◽

Selection Methods ◽

Low Mass ◽

Future Work

ABSTRACT This study aims to explore the relation between dwarf galaxies (M* ≤ 5 × 109 M⊙) with active galactic nuclei (AGNs) and their environment by comparing neighbourhood parameters of AGN and non-AGN samples. Using the NASA-Sloan Atlas, both the local environment and the immediate environment of dwarf galaxies with z ≤ 0.055 are analysed. Of the 145 155 galaxies in the catalogue, 62 258 of them are classified as dwarf galaxies, and by employing two AGN selection methods based on emission-line fluxes (BPT and WHAN), 4476 are found to have AGN characteristics in their optical spectra. Regardless of selection method, this study finds no discernible differences in environment between AGN and non-AGN host dwarf galaxies and these results indicate that environment is not an important factor in triggering AGN activity in dwarf galaxies. This is in line with existing literature on environments of regular galaxies with AGNs and suggests universality in terms of reaction to environment across the mass regime. The biases of AGN selection in low-mass galaxies, and the biases of different measures of environment are also considered. It is found that there are several mass trends in emission-line ratios and that the SDSS fibre covers galaxies non-uniformly with redshift. These biases should be accounted for in future work by possibly including other wavelength regimes or mass weighting of emission-line ratios. Lastly, a discussion of the environment estimation methods is included since they may not gauge the desired properties due to factors such as time delay or using loosely constrained proxy parameters.

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State-of-the-art AGN SEDs for photoionization models: BLR predictions confront the observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1207 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5917-5922 ◽

Cited By ~ 3

Author(s):

G J Ferland ◽

C Done ◽

C Jin ◽

H Landt ◽

M J Ward

Keyword(s):

Emission Line ◽

Active Galactic Nuclei ◽

Spectral Energy Distribution ◽

Galactic Nuclei ◽

Spectral Energy ◽

X Ray ◽

Line Region ◽

Energy Conserving ◽

Far Ultraviolet ◽

New Generation

ABSTRACT The great power offered by photoionization models of active galactic nuclei emission line regions has long been mitigated by the fact that very little is known about the spectral energy distribution (SED) between the Lyman limit, where intervening absorption becomes a problem, and 0.3 keV, where soft X-ray observations become possible. The emission lines themselves can, to some degree, be used to probe the SED, but only in the broadest terms. This paper employs a new generation of theoretical SEDs that are internally self-consistent, energy conserving, and tested against observations, to infer properties of the emission-line regions. The SEDs are given as a function of the Eddington ratio, allowing emission-line correlations to be investigated on a fundamental basis. We apply the simplest possible tests, based on the foundations of photoionization theory, to investigate the implications for the geometry of the emission-line region. The SEDs become more far-ultraviolet bright as the Eddington ratio increases, so the equivalent widths of recombination lines should also become larger, an effect that we quantify. The observed lack of correlation between Eddington ratio and equivalent width shows that the cloud covering factor must decrease as Eddington ratio increases. This would be consistent with recent models proposing that the broad-line region is a failed dusty wind off the accretion disc.

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