Dust in the sub-mm or: what is  ?

Dust in the sub-mmor: what is  ? B. T. Draine PrincetonUniversity 2005 June 14 B.T. Draine: Dust in the submm

mm Radiation from Dust:Emission Mechanisms • Thermal fluctuations in charge distribution: “vibrational emission”. Dominant emission mechanism for >90 GHz • Rotational emission from Spinning Dust Grains (Draine & Lazarian 1998): dominant emission mechanism for <60 GHz in ISM • Thermal fluctuations in magnetization? (Draine & Lazarian 1999): important for <90 GHz IF ferromagnetic grains present B.T. Draine: Dust in the submm

Microwave Emission • Dust-correlated microwave emission discovered by CMB studies. • Likely due to spinningdust (Draine & Lazarian 1998) -- same ultrasmall dust grains needed to explain 3-15um “PAH” emission. • Dense clouds and CS disks may have low abundance of ultrasmall grains: if so, dust rotational emission not important even in microwave. Draine 2003 B.T. Draine: Dust in the submm

Watson et al 2005 astroph/0503714v1 cloud in Perseus B.T. Draine: Dust in the submm

Magnetic Dipole Emission from Magnetic Grains If grains are • ferromagnetic (e.g., metallic Fe) or • ferrimagnetic (e.g., magnetite Fe3O4) Then thermal fluctuations in magnetization will result in strong emission at <90 GHz (Draine & Lazarian 1999). Do not know amounts of Fe in different chemical forms: magnetic materials could be abundant enough to be important Unimportant for f > 100GHz. B.T. Draine: Dust in the submm

Vibrational Emission from Dust B.T. Draine: Dust in the submm

Laboratorydata for amorphous solids: B.T. Draine: Dust in the submm

Interstellar Dust Opacities • Dust model (Weingartner & Draine 2001; Li & Draine 2001) Mixture of • amorphous silicate • carbonaceous grains • PAHs = smallest carbonaceous grains • Submm dielectric function for amorphous silicate adjusted to reproduce COBE FIRAS observations of ISM Model reproduces: • Observed extinction from IR to UV • Observed emission from submm to IR B.T. Draine: Dust in the submm

B.T. Draine: Dust in the submm

Modeling IR Emission • Physical grain model: Cabs() , heat capacity • Stochastic heating: Find p(T; comp,size) for each composition, size • Time-averaged IR emission: P =  dT p(T) Cabs() 4 B(T) • Sum over compositions, size distribution B.T. Draine: Dust in the submm

Modeling IR Emission from Interstellar Dust 100 x Local ISRF 1 x Local ISRF B.T. Draine: Dust in the submm

IR Emission Calculated for Model Galaxy spectrum = weighted average of such spectra B.T. Draine: Dust in the submm Li & Draine (2001)

IR View NGC 7331 3.6m: starlight 8.0m: dustglow B.T. Draine: Dust in the submm

NGC 7331(Regan et al. 2004) B.T. Draine: Dust in the submm

Dust in NGC 7331 • Same grain model (Li & Draine 2001) as used for Milky Way • Umin = 0.3, Umax = 104 ( local ISRF) • most of power is from dust heated by U < 2 • ~12% of power from dust heated by U>102 B.T. Draine: Dust in the submm

Regan et al (2004) NGC 7331 Spectrum: Observations and Model r<4kpc • Upper: Ring and interior. • Lower: Entire galaxy • Black curve and red triangles: starlight + Li & Draine dust model for MW dust • Md= 3x108M  Mgas= 5x1010M (total) • Mgas in agreement with HI and CO observations • 450um,850um flux agrees with model:WD01submm opacity is OK entire galaxy B.T. Draine: Dust in the submm

Submm Dust Opacities • WD01 dust opacities (with  in FIR) appear to reproduce global emission from galaxies: if additional exotic grains present, not important in global energetics • Submm observations of Orion-KL: consistent with (Beuther et al 2004) B.T. Draine: Dust in the submm

Submm Spectra of Circumstellar Disks/YSOs • F   • Optically-thin, Rayleigh-Jeans:  = 2+ where    • Observe: 3 (e.g., Beckwith & Sargent 1991; Hogerheidje et al 2003, Beuther et al 2004; Andrews & Williams 2005 [astro-ph/0506187]) • Therefore: 1 ? • What does this imply about dust in YSOs? B.T. Draine: Dust in the submm

Why do YSOs have 3 ? Three logical possibilities: • Perhaps YSO dust material has  such that small particles have    -- dust in disk made of different material than dust in ISM? [or perhaps “fractal grains”?…. ] • Perhaps inner parts of YSO dust disks are optically thick, in which case  • Grain growth in disk: B.T. Draine: Dust in the submm

Grain Growth in Disk… • Coagulation: Fluffy particles may have increased opacities. Stognienko, Henning & Ossenkopf (1995, 1996) found 2 at m. (ISM grains may also be expected to be coagulated structures). • Some grains may be large enough so that grain is not in small particle limit. Because grain growth is expected, size might be most natural explanation…. B.T. Draine: Dust in the submm

Effects of Grain Growth Consider power-law size dist., dn/da a-3.5 (most of area in small grains, most of mass in large grains). Nature likes this size distribution… Calculate opacity for different amax for spherical grains with same composition as in WD01 model for dust in ISM. B.T. Draine: Dust in the submm

Increase amax from 0.25m (ISM dust) to 1m. • Small increase in  as result of magnetic dipole absorption in carbonaceous grains (eddy currents) B.T. Draine: Dust in the submm

Further increase amax… B.T. Draine: Dust in the submm

This size distribution gives opacity varying approximately as 1 in submm, once grain growth reaches amax > 1mm. (submm)  amax-0.5 B.T. Draine: Dust in the submm

Summary • Rotational emission from very small grains and magnetic dipole emission from magnetic dust is unimportant in submm • Global submm emission from normal galaxies is approximately consistent with WD01 dust opacity (submm  1.7) • YSOs and CS disks with 1 can plausibly be explained using standard interstellar grain materials if grain growth to > mm sizes. Exotic grain materials not required. B.T. Draine: Dust in the submm

Starlight Dustglow THANK YOU B.T. Draine: Dust in the submm

Dust in the sub-mm or: what is  ?