1

Dusty Torus Formation by Anisotropic Radiative Feedback of

Active Galactic Nuclei

Shuang-Nan Zhang, Yuan Liu, Jin Zhang

Institute of High Energy Physicsand

National Astronomical Observatories of ChinaChinese Academy of Sciences

Liu,Y. & Zhang, S.N., 2011, ApJL, 728, L44

2/22

The unified model of AGN

Dusty torus

Formation？

Evolution？

3/22

AGN feedback The distribution of the dust

is anisotropic The UV/optical radiation

from the accretion disk is also anisotropic

The effect of radiation pressure is significant due to the presence of dust

The normal of the accretion disk

( ) cos( )f Observer & dust

A~500

4/22

The evolution of AGNs

A B C

Momentum effect of radiation

5/22

Evaporation radiusThe inner radius of dust

Energy effect of radiation

6/22

10-3

10-2

10-1

100

10-10

100

1010

1020

r (pc)

t (s

)

Torus formation time scale: ~105-6 yr for 10 pc

a： dust radius

L=1044 erg/s; L/LEdd=0.1; a=0.1 m; A=100

1 year

Hot low density gas:Seed for BLR? Empty

Vertical distance from the disk Z (pc)

Radiation pressure

Evaporation

~0.2 ly

7/22

The profile of a dusty torus

8/22

NH-L/LEdd plane

Raimundo, Fabian, Bauer et al. 2010

9/22

The fraction of type 2 AGNs

Hasinger 2008

M L

10/22

The inner radius of dusty torus

-23 -22 -21 -20 -19 -18 -17 -161

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

MV

log

(d

ays

)

Suganuma et al. 2006

11/22

The evolution of dusty torusLuminous, with torus, but without bright BLR

105-6 yr

?

High density clouds

Low density

gas

12/22

Weak line quasars

Shemmer et al. 2009; EW<5 A; continuum similar to normal quasars

13/22

Radio quiet BL Lac

Plotkin et al. 2009

No obvious emission lines

14/22

Are WLQs and Radio Quiet BL Lac the Objects Predicted by Our Model?

Predictions Luminous accretion disk emission Existence of Dusty Torus

Tests Low polarization disk not jet Low variability disk not jet Hot dust emission torus illuminated by luminous

disk

15/22

Very low polarization in continuum spectra: only two of 25 candidates are observed with weak polarization (Heidt & Nilsson 2011); non detection for all others

The continuum spectrum is consistent with disk origin

Polarization Test: radio quiet BL Lac

16/22

Long Term Variability Test So far observ

ations are quite limited

Weaker than radio loud BL Lac？

Need more observations

Plotkin et al. 2010

17/22

Long Term Variability Test SDSS Stripe 82（ 12 radio quiet BL Lac， 4 WL

Q， 27 radio loud BL Lac）

5.1 5.15 5.2 5.25 5.3 5.35 5.4 5.45

x 104

19.6

19.7

19.8

19.9

20

20.1

20.2

20.3

20.4

20.5

025612.47-001057.8

r

MJD5.1 5.15 5.2 5.25 5.3 5.35 5.4 5.45

x 104

18.6

18.8

19

19.2

19.4

19.6

19.8

003808.50+001336.5

MJD

r

Radio quiet Radio loud

18/22

Lightcurve amplitudes

17 17.5 18 18.5 19 19.5 20 20.510

0

101

102

103

104

r (SDSS)

2/DOF

Radio loud

Radio quiet

19/22

Four SDSS Radio Quiet BL Lac Observed with Lijiang 2.4 m at V, I and R bands

SDSS 094533.99+100950.1 081250.80+522530.8

085025.60+342750.9 090107.64+384658.8

SDSS 094533.99+100950.1

085025.60+342750.9

20/22

Very weak short timescale variability! Time (Hour)

m(B

L La

c)-m

(Sta

r)

2 / DOF=7.3/15 2 / DOF=20.1/26

2 / DOF=24.8/192 / DOF=38.3/25

Short Term Variability Test

21/22

Hot Dust Test in weak line quasars

Black body from hot dust

Diamond-Stanic et al. 2009

Evidence of hot dust in WLQ

22/22

Conclusions The distribution of dusty gas should also be anisotropic due

to the influence of the anisotropic disk radiation. Our model can explain the presence of some obscured

AGNs with high Eddington ratios and can also reproduce the observed decreasing fraction of type 2 AGNs with increasing luminosity.

Our model predicts the existence of luminous AGNs with dusty tori, but without luminous broad line regions. Weak line quasars and radio quiet BL Lac?

Weak polarization, low variability and hot dust feature confirm our model predictions.

Liu,Y. & Zhang, S.N., 2011, ApJL, 728, L44