Frank IsraelSterrewacht Leiden

ANOMALOUS DUST IN LATE TYPE

GALAXIES

COSMIC DUST:

EASY TO SEE, HARD TO GAUGE ...

SED (Continuum Spectrum) Analysis

Dust parameters from dust emission assuming(large) dust grains in thermal equilibrium and

emitting as modified blackbodies

Iv

= Nd

(c / )- Bv(T)

==> , composition (opacity, emissivity),

temperature, amount--- important degeneracies: N- and -T

dust emits at 10-300 microns (MIR, FIR)

IRAS (1983) SURVEY FIRST GLOBAL IR(12–100 μm) FLUXES FROM ~11000

GALAXIES

a. large amounts of warm dust ubiquitous

b. missing IR peak intensity

c. no information on cold dust (<15 K)

d. potentially large dust mass unsampled

Need coverage >100 μ m

ISO (1995-1998): up to 175 (240) μm

Spitzer (2003-2009): up to 160 μm

Herschel (2009-): up to 500 μm

a. define peak (temperature Td)

b. suggest RJ slope (emissivity )

Dust emissivity ?

Crystalline Silicate: = 2.0Amorphous Graphite: = 1.0

change with temperature, frequency range(Jones 2002; Meny et al. 2007)

Empirical Milky Way dust:(Dupac et al. 2003; Desert et al. 2008)

T = 13 K ==> = 2T = 30 K ==> = 1

Dust emissivity

Empirical MW dust:(Dupac et al. 2003; Desert et al. 2008)

(cold dust) is not 2!

More sophisticated dust emission models(Zubko, Dwek, Draine, Li and others)

MAJOR COMPLICATION # 1

Degeneracy of long-wavelength SEDs!

Herschel Heritage Program LMC

Meixner et al. 2010Herschel Hermes Program M33

Kramer et al. 2010

MW vs LMC and M33similar FIR SED

different dust

MAJOR COMPavelength SEDs!

Herschel Heritage Program LMCGalliano 2010

SED fits identical up to 500 μmbut dust mass differs by factor ~4

Degeneracy of long-wavelength SEDs

MW, M33, and LMC similar FIR SEDdifferent metallicities:

MW = 1, M33 = 0.5; LMC = 0.4

Inferred dust-to-gas ratios:

MW (silicate, graphite): 1/150M33 (silicate, graphite): 1/40LMC (silicate, graphite): 1/65

LMC (silicate, amorphous carbon): 1/287

Add submm data points: drops with approaching unity longwards 500 μm

GC 1569 starburst dwarf galaxy SED:very cold or very small dust grains?

W

LMC and SMC: WMAP and COBE data added (Israel et al. 2010 )

mm emission excess:

Israel et al. 2010 (ArXiv1006.2232)

Bot et al. 2010 (ArViv1008.2875)

MAJOR COMPLICATION # 2

In SMC and LMC, cold dust cannot explainobserved (sub)millimeter wavelength SED

Occurrence of anomalous emission:

Very Small Grains (VSG) (Lisenfeld et al. 2002)

Disordered Charge Distribution (DCD)and/or Two-Level Systems (TLS) in Amorphous Dust Grains (Paradis 2007)

Spinning Dust (Draine & Lazarian 1998)

LMC (Bot et al. 2010) SMC

In SMC and LMC, anomalous mmemission is best explained by

spinning dust grains.

Emission enhanced but no mass contribution!

Other galaxies?

Adequate coverage of cm to submm (10-500

GHz) range is rare

WMAP: NGC 253,M82,NGC 4945

Groundbased: a fewarchetypes such asArp 220, IIZw40

Anomalous Dust Emission:

mm fluxes lacking

FIR/submm slopes:

β = 1.50 +/- 0.06 (30 galaxies) β = 1.08 +/- 0.17 (6 dwarfs)

'excess' in all magellanic irregulars?

Anomalous Dust Emission:

Milky Way: 'Cold' component(Reach et al. 1995, Draine & Lazarian 1998)

SMC and LMC(Israel et al. 2010, Bot et al. 2010)

NGC 6946(Murphy et al. 2010)

M82? Irregular Dwarfs? M33?

SUMMARY

opacity and emissivity still poorly known

Dust models degenerate at λ < 500 μm FIR

No 'universal' dust

Anomalous emission at 500μm<λ<2cm(sub)mm – cm

SED degeneracy and contamination rule out identification of cold dust (T<15K)

CONCLUSIONS

in other galaxies:mass of warm dust uncertain

mass of cold dust undetermined

dust- to-gas ratio and dust mass presently undetermined

urgent need for better insight indust grain properties

Workshop

Herschel and the Nature of Dust

Lorentz Center

Leiden University, Netherlands

February 28 th to March 4th