INfluence of turbulence on extinction in various

environments

Huirong Yan

KIAA-PKU

Collaboration: H. Hirashita, A. Lazarian, T. Nazowa, T. Kazasa

Why do we care?

Gordon et al. 2003

cf. Kudritzki

cf. PNNL

Grain size distribution is determined by their dynamics

• radiation field: radiation pressure photoelectric force, photodesorption,

• H2 thrust

• Gaseous drag

• shock acceleration

• Brownian motions

Processes considered in earlier literature

Turbulence is ubiquitous

Re < 1

Re ~ 40

Re ~ 104

www-pgss.mcs.cmu.edu

Reynolds number: Re≡ LV/ν

Extended Big Power Law

Armstrong et al. (1995), Chepurnov & Lazarian (2009)

Re>>1Observational evidence

Astrophysical fluid is turbulent

Grains are charged!

Grains in many cases are magnetized!

Resonance mechnism

Gyroresonanceω- k||v|| = nΩ(n = ± 1, ± 2 …),Which states that the MHD wave frequency (Doppler shifted) is a multiple of gyrofrequency of particles (v|| is particle speed parallel to B).

BB

Tested model of MHD turbulence

Alfven slow fast~k-5/3 ~k-5/3 ~k-3/2

anisotropic (GS)

anisotropic (GS)

isotropic

Contours of equal correlation are shown

anisotropyanisotropy

Cho & Lazarian (2002)

Examples of MHD perturbations Examples of MHD perturbations (P(Pmagmag > P > Pgasgas) )

Examples of MHD perturbations Examples of MHD perturbations (P(Pmagmag > P > Pgasgas) )

Alfven mode (v=VA cosθ)incompressible;

restoring force=mag. tension

kk

BB

slow mode (v=cs cosθ)

fast mode (v=VA)restoring force = Pmag + Pgas

BBkk

BB

restoring force = |Pmag-Pgas|

Gyroresonanceω- k||v|| = nΩ(n = ± 1, ± 2 …),Which states that the MHD wave frequency (Doppler shifted) is a multiple of gyrofrequency of particles (v || is particle speed parallel to B).

So, k||,res~ Ω/v = 1/rL

Resonance mechanismResonance mechanism

BBrL

Betatron Acceleration by CompressibleTurbulence

Traditionally, Betatron acceleration was only considered behind shocks. Turbulence, however, can also compress the magnetic field and therefore accelerate dust through the induced electric field.

Dust dynamics is dominated by MHD turbulence!

Grains can reach supersonic speed due to acceleration by turbulence and this results in more efficient shattering and adsorption of heavy elements (Yan & Lazarian 2003, Yan 2009).

velo

city

of

charg

ed g

rain

s

Grain size

1km/s!1km/s!

Shattering of grains

What are the implications for interstellar dust?

Extinction curve varies according to local Conditions of turbulence (Hirachita & Yan 2009).

Extinction curveEvolving grain size distribution in turbulence

50 Myr100 Myr

50 Myr100 Myr

initial

Grain velocity in starburst galaxies

Grains reach higher speeds because of enhanced turbulence!

Grain size distribution

Extinction curves in starburst galaxies

Extinction in starburst galaxies (Cont.)

UV band

Summary

Changes in the MHD turbulence paradigm result in Changes in the MHD turbulence paradigm result in revision of theories of physical processes in ISM. revision of theories of physical processes in ISM.

The dynamics of dust in general ISM is dominated The dynamics of dust in general ISM is dominated by turbulence. by turbulence. Dust can get supersonic via interactions with interstellar turbulence. The velocities obtained are sufficiently high to be important for influencing metallicity and ionization in ISM.

Cosmic ray cross field transport is determined by Cosmic ray cross field transport is determined by turbulence. turbulence. 1. Perpendicular motion is diffusive. Suppression of ⊥ diffusion depends on the level of turbulence, MA ≣δB/B0

2. This affects diffuse gamma ray emission, CMB foreground , etc.

Shock acceleration is influenced by preexisting Shock acceleration is influenced by preexisting turbulence. turbulence.