CfA B.T. Draine: Dust in the submm1 Dust in the sub-mm or: what is  ? B. T. Draine Princeton University 2005 June 14

CfA B.T. Draine: Dust in the submm2 mm Radiation from Dust: Emission Mechanisms 1.Thermal fluctuations in charge distribution: “vibrational emission”. Dominant emission mechanism for >90 GHz 2. Rotational emission from Spinning Dust Grains (Draine & Lazarian 1998): dominant emission mechanism for <60 GHz in ISM 3. Thermal fluctuations in magnetization? (Draine & Lazarian 1999): important for <90 GHz IF ferromagnetic grains present

CfA B.T. Draine: Dust in the submm3 Microwave Emission Dust-correlated microwave emission discovered by CMB studies. Likely due to spinning dust (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

CfA B.T. Draine: Dust in the submm4 Watson et al 2005 astroph/ v1 cloud in Perseus

CfA B.T. Draine: Dust in the submm5 Magnetic Dipole Emission from Magnetic Grains If grains are ferromagnetic (e.g., metallic Fe) or ferrimagnetic (e.g., magnetite Fe 3 O 4 ) 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.

CfA B.T. Draine: Dust in the submm6 Vibrational Emission from Dust

CfA B.T. Draine: Dust in the submm7 Laboratory data for amorphous solids:

CfA B.T. Draine: Dust in the submm8 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

CfA B.T. Draine: Dust in the submm9

CfA B.T. Draine: Dust in the submm10 Modeling IR Emission Physical grain model: C abs ( ), heat capacity Stochastic heating: Find p(T; comp,size) for each composition, size Time-averaged IR emission: P =  dT p(T) C abs ( ) 4  B (T) Sum over compositions, size distribution

CfA B.T. Draine: Dust in the submm11 Modeling IR Emission from Interstellar Dust 1 x Local ISRF 100 x Local ISRF

CfA B.T. Draine: Dust in the submm12 IR Emission Calculated for Model Li & Draine (2001) Galaxy spectrum = weighted average of such spectra

CfA B.T. Draine: Dust in the submm13 IR View NGC  m: starlight 8.0  m: dustglow

CfA B.T. Draine: Dust in the submm14 NGC 7331 (Regan et al. 2004)

CfA B.T. Draine: Dust in the submm15 Dust in NGC 7331 Same grain model (Li & Draine 2001) as used for Milky Way U min = 0.3, U max = 10 4 (  local ISRF) most of power is from dust heated by U < 2 ~12% of power from dust heated by U>10 2

CfA B.T. Draine: Dust in the submm16 NGC 7331 Spectrum: Observations and Model Upper: Ring and interior. Lower: Entire galaxy Black curve and red triangles: starlight + Li & Draine dust model for MW dust M d = 3x10 8 M   M gas = 5x10 10 M  (total) M gas in agreement with HI and CO observations 450um,850um flux agrees with model: WD01 submm opacity is OK r<4kpc entire galaxy Regan et al (2004)

CfA B.T. Draine: Dust in the submm17 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)

CfA B.T. Draine: Dust in the submm18 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/ ]) Therefore:  1 ? What does this imply about dust in YSOs?

CfA B.T. Draine: Dust in the submm19 Why do YSOs have  3 ? Three logical possibilities: 1.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”?…. ] 2.Perhaps inner parts of YSO dust disks are optically thick, in which case  3.Grain growth in disk:

CfA B.T. Draine: Dust in the submm20 Grain Growth in Disk… 1.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). 2.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….

CfA B.T. Draine: Dust in the submm21 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 a max for spherical grains with same composition as in WD01 model for dust in ISM.

CfA B.T. Draine: Dust in the submm22 Increase a max from 0.25  m (ISM dust) to 1  m. Small increase in  as result of magnetic dipole absorption in carbonaceous grains (eddy currents)

CfA B.T. Draine: Dust in the submm23 Further increase a max …

CfA B.T. Draine: Dust in the submm24 This size distribution gives opacity varying approximately as 1 in submm, once grain growth reaches a max > 1mm.  (submm)  a max -0.5

CfA B.T. Draine: Dust in the submm25 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.

CfA B.T. Draine: Dust in the submm26 StarlightDustglow THANK YOU