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 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 ~ 10 4 www-pgss.mcs.cmu.edu Reynolds number: Re≡ LV/ν

Extended Big Power Law Armstrong et al. (1995), Chepurnov & Lazarian (2009) Re>>1 Observational evidence Astrophysical fluid is turbulent

Grains are charged! Grains in many cases are magnetized!

Resonance mechnism Gyroresonance  - k || v || = n  (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). B

Tested model of MHD turbulence Alfven slowfast ~k -5/3 ~k -3/2 anisotropic (GS) isotropic Contours of equal correlation are shown anisotropy Cho & Lazarian (2002)

Examples of MHD perturbations (P mag > P gas ) Alfven mode (v=V A cos  ) incompressible; restoring force=mag. tension k B slow mode (v=c s cos  ) fast mode (v=V A ) restoring force = P mag + P gas B k B restoring force = |P mag -P gas |

Gyroresonance  - k || v || = n  (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 ~ /v = 1/r L Resonance mechanism B rLrL

Betatron Acceleration by Compressible Turbulence 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 ). velocity of charged grains Grain size 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 curve Evolving grain size distribution in turbulence 50 Myr 100 Myr 50 Myr 100 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 revision of theories of physical processes in ISM. The dynamics of dust in general ISM is dominated by turbulence. The dynamics of dust in general ISM is dominated 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 turbulence. Cosmic ray cross field transport is determined by turbulence. 1. Perpendicular motion is diffusive. Suppression of  diffusion depends on the level of turbulence, M A ≣  B/B 0 2. This affects diffuse gamma ray emission, CMB foreground, etc. Shock acceleration is influenced by preexisting turbulence.