1. 星际物理与化学（大连）讨论会
Dust in the Local Group, AGNs, and High-z Universe Aigen Li (University of Missouri)
16 - July -2014

2. Collaborators: Biwei Jiang, Jian Gao, Shu Wang
星际气体各具特色，星际尘埃独领风骚。。。

3. External organic dust removed
Dust controls the appearance of old stars…
Rich in organic dust
External organic dust removed

4. FOCUS Dust in the Local Group
Dust in the Milky Way: Size, Composition as derived from extinction and IR emission
Dust in the Local Group
Dust in AGNs: Size, Composition  Are all AGNs born equal?
Dust at high-z
Summary

5. To start: dust = small solid grains, their sizes extend over 3 orders of magnitudes, from a few Å to nm to a few m

6. “Surely, there is a hole in the heaven…” (Sir William Herschel 1785)
Dust blocks the light emitted by background stars
The Milky Way
dark patches, rifts: obscuration of a high concentration of dust

7. Gas and dust in interstellar space: The interstellar medium (ISM)

8. Power: in the local Universe, energy of IR/submm background = energy of optical back ground  nearly half of the optical light emitted since the Big Bang has been absorbed and re-radiated in the IR by dust!

9. A few more facts about interstellar dust ….
The sizes of dust particles extend over ~3 orders of magnitude, from ~1 nm to ~1µm
Dust composition is strongly constrained by cosmic abundance of chemical elements: oxygen-rich (silicates, metal oxides) and carbon-rich compounds.
Dust plays important roles in star formation and in the physics and chemistry of the interstellar gas.

10. Interstellar extinction  “pair” method: compare spectra of 2 stars with same spectral type, with one star nearby and unreddened

11. Galactic Interstellar Extinction: Grain Size
2 grain populations:
a < 100 Å;
a>0.1 µm;
Characterized by RV=AV/E(B-V);
dense regions: larger RV;
larger RV  larger grains;
2175 Å bump
aromatic carbon;
small graphitic grains or PAHs;
高健／王舒报告

12. cold dust
warm dust
PAHs
COBE=Cosmic Background Explorer

13. nano grains/PAHs with a<10nm
important contribution to ultraviolet (UV) extinction;
Single starlight photon heated to T»20K, undergo “temperature fluctuation”;
responsible for the IR emission at λ<60 µm;
~35% of emitted power;
PAHs ← 3.3, 6.2, 7.7, 8.6, 11.3µm emission features

14. polycyclic aromatic hydrocarbon = PAH
fused benzene rings
3.3µm: C-H stretching mode;
6.2, 7.7µm: C-C stretching modes;
8.6µm: C-H in-plane bending mode;
11.3, 12.7µm: C-H out-of-plane bending modes;
Li & Draine2001, Draine & Li 2007: NC ~ 100

15. Interstellar Polarization
李祺报告
Large grains
nonspherical and
aligned
Small grains
spherical and/or
not aligned;

17. Presolar grains in meteorites: interstellar origin
graphite
nano TiC
nanodiamond
Li & Mann 2012
Presolar grains in meteorites: interstellar origin

18. Interstellar Dust in Solar system
Presolar grains in meteorites
(Hoppe & Zinner 2000; Draine 2003)
composition
diameter (µm)
abundance
origins
diamond
0.002
5E-4 SN
SiC
0.3-20
6E-6
AGB
graphite
1-20
1E-6
AGB,SNII,nova
Al2O3
0.5-3
3E-8
RG,AGB
Si3N4 ~1
2E-9
SNII

19. Interstellar Extinction: Mid-Infrared
Since the development of observation in infrared(IR), the classic silicate-graphite model with power-law
size distribution does not work very well for interpreting these mid-IR results.
Neither MRN nor WD01 (RV =3.1) could explain the observed flat, “gray” mid-IR extinction!

20. Evidence for µm-size dust?
Wang, Li, & Jiang 2014

21. Dust in Local Galaxies Far-UV extinction, 2175Å bump → dust size and composition different!

22. Dust in Local Galaxies IR emission: little “PAH” emission in SMC …
Li & Draine 2002
SMC

23. Interstellar Extinction in M31
李王姜高2014
M31
LMC2

24. The CCM formula: very nice: knowing RV=AV/(AB-AV),
the entire extinction curve is known! But this does not
apply to external galaxies, even not for LMC, SMC!
Liang & Li

25. Dust in AGNs
Dust plays an important role in the “Unified Theory of AGNs”;
orientation-dependent obscuration by dust torus  Seyfert 1 vs. Seyfert 2;
IR emission accounts for ~10% of the bolometric luminosity of Type 1 AGNs, >50% of Type 2;
Heated dust  IR emission;
IR emission modeling  circumnuclear structure (critical to the growth of supermassive black hole);

26. AGN = active galactic nuclei
Antonucci
1993
Type 1
Type 2
2175 Å
Urry &
Padovani
1995
2175 Å

27. AGN Dust Compsoition Silicate dust: a wide diversity of compositions
Carbon dust: 3.4μm C-H stretching absorption feature seen in AGN dust torus
PAHs: not seen in AGNs ← X-ray photons destroy PAHs
Ices: not seen in AGNs ← T>100K even at 100pc from the central engine  ice sublimates

28. AGN Dust Extinction: flat/gray?  large grains?
Czerny et al. (2004): 5 SDSS composite quasar spectra flat extinction
Gaskell et al. (2004): 72 radio-loud, 1018 radio-quiet AGNsflat extinction
AGN
Dust coagulational growth?
AGN
Preferential destruction
of small dust?
Li 2007

29. AGN slicates differ from Milky Way ISM?
9.7mm silicate feature: “red” shifted & broadened (Hao et al. 2005, Sturm et al. 2005): different composition? Rad.transf. effects?
Li et al. (2008): porous, large grains  “red-shifting” and broadening the silicate feature?
邵珍珍报告

30. Dust in the High-Redshift Universe
Dust is seen in (almost) all high-z sources: quasars, GRBs, submm galaxies, DLAs …
Reddening and obscuration
IR to mm emission
Depletion of heavy elements
Whether the dust properties vary with z?

31. 2175Å bump in the distant universe
Intervening absorption systems toward distant quasars (Wang et al. 1994, Inou et al. 2006, Srianand et al. 2008, York et al. 2008, Conroy et al. 2010, Zhou et al. 2010, Jiang et al …)
Distant UV-attenuated galaxies (Noll & Pierini 2005, Noll et al. 2007, 2009)
Gravitational lensing galaxies
Damped Ly Absorbers
Gamma-Ray Burst (GRB) host galaxies

32. 2175Å bump in Gama Ray Burst (GRB) Host Galaxies GRB 070802: z=2
2175Å bump in Gama Ray Burst (GRB) Host Galaxies GRB : z=2.45, AV ~ 1mag
Kruehler et al. 2008
Eliasdottir et al. 2009

33. PAHs at z=4
Riechers et al. (2014)

34. The Sources of Dust z<5 (age > 1 Gyr): AGB Stars
At local universe, the major source of dust are the envelopes of AGB stars, which require about 1 Gyr to evolve.
z > 5 (age < 1 Gyr): SNe
Supernova origin for dust
in high-z quasar
(Maiolino et al. 2004, Nature)
Supernova also origin for dust in high-z GRBs (?)

35. Dust Properties as a Function of Redshifts
AV: dust quantity
Far-UV extinction (c1): small grains
2175Å bump (c4): sp2 carbon
RV: indicative of grain size
Silicate vs carbon dust (e.g. graphite): at high z carbon dust not efficiently made? → mgra/(msil+mgra) decreases with z?
Mean grain size <a>: at high z, less raw material→ small <a>; supernovae destruction → large <a> …

36. Extragalactic dust through GRBs --- 67 GRBs at 0<z < 7.0
(Liang & Li 2011)

37. Summary
Dust in AGNs: obscuration correction; probing physical conditions & circumnuclear structure;
Dust extinction: flat, “gray”  large dust grains;
No 2175Å extinction bump  small graphitic grains destroyed?
Silicates: very different from Galactic silicate dust;
Carbon dust: 3.4μm absorption feature closely resembles that of Milky Way
No Ices  AGN torus too warm so that water ice sublimates;
No PAHs  X-ray/UV photons destroy PAHs;

38. Summary
Caution should be taken in using the CCM formula to calculate external extinction.
The extinction curves of GRB host galaxies can differ substantially from the known MW/LMC/SMC extinction laws.
The 2175Å extinction feature appears to be present at all redshifts.
There does not appear to show any evidence for a dependence of dust extinction on redshifts.
No obvious evidence to show dust properties are different between z < 5 and z > 5.

39. Modeling IR Emission
For a grain model: Cabs() , heat capacity
Stochastic heating:
find dP/dT (T; comp,size) for each composition, size
Time-averaged IR emission:
P =  dT dP/dT(T) Cabs() 4 B(T)
Sum over compositions, size distribution
Nano dust: heat capacity < energy of a single photon!
1day = 8.64E4 s
temperature fluctuation

40. Temperature Fluctuation of Nanoparticles
Li & Mann 2012

41. Av / Δτ9.7 ≈ 6.4
Av / Δτ9.7 ≈ 9.0
Av / Δτ9.7 ≈ 18.5
Lyu, Hao & Li (2014)

42. (Av / Δτ9.7)AGN ≈ 6.4 << (Av / Δτ9.7)MW ≈ 18.5
Lyu, Hao & Li (2014)
Large dust ?
(Av / Δτ9.7)AGN ≈ << (Av / Δτ9.7)MW ≈ 18.5
Dust coagulation growth
Preferential destruction of small dust grains

43. Compared with observed afterglow SEDs
Determining dust extinction of GRB host galaxies from afterglow spectral energy distributions
Compared with observed afterglow SEDs
Example:

44. Extragalactic dust through GRBs --- 67 GRBs at 0<z < 7.0
Dust-to-gas ratios
extinction Av vs. z
No strong evidence for the dependence of Av on z.
Liang & Li 2011

45. Dust Properties as a Function of Redshifts
AV: dust quantity
Far-UV extinction (c1): small grains
2175Å bump (c4): sp2 carbon
RV: indicative of grain size
Silicate vs carbon dust (e.g. graphite): at high z carbon dust not efficiently made? → mgra/(msil+mgra) decreases with z?
Mean grain size <a>: at high z, less raw material→ small <a>; supernovae destruction → large <a> …

46. Extragalactic dust through GRBs --- 67 GRBs at 0<z < 7.0
(Liang & Li 2011)

47. Dust Properties as a Function of Metallicity
AV:  metallicity ?
Far-UV extinction (c1): small grains  metallicity ?
2175Å bump (c4): low metallicity → weak bump?

48. Extragalactic dust through GRBs --- 67 GRBs at 0<z < 7.0
(Liang & Li 2011)