Dust and molecules in spiral galaxies as seen with the jcmt



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DUST AND MOLECULES IN SPIRAL GALAXIES as seen with the JCMT

    • F.P. Israel, Sterrewacht Leiden

ATOMS and MOLECULES ...



... AND DUST

  • SCUBA 850 mu



M51 Line and Continuum





M51 J=3-2 CO depleted in center, enhanced in arms



ISM in Spiral Galaxies

  • Atomic gas avoids center

  • Molecular gas often concentrated in center

  • Dust emission follows total gas

  • Metallicity & excitation gradients

  • Center: exclusively molecular

  • Inner disk: molecules dominant

  • Outer disk: atoms dominant





Nuclear CO concentrations disk, torus or spiral?



12CO degeneracy resolved by 13co



Molecules in galaxy centers

  • Concentrated within R = 0.5 kpc

  • High contrast with disk CO

  • CO pollutes broadband continuum!

  • Physical parameters only from several line transitions!

  • At least two components:

  • Lukewarm and dense

  • Hot and tenuous

  • Hot and tenuous gas >50% of mass



Dust in galaxy centers

  • heating/cooling depends on:

  • dust grain composition

  • dust grain size (distribution)

  • Radiation, shocks, turbulence



The AGN in CENA



M83



NGC 6946, NGC 891 1



Origin of Subm/FIR emission: NGC 6822

  • Israel, Bontekoe & Kester, 1996



Dust-to-gas ratios

  • Dependent on metallicity, but how ?

  • log [O]/[H] = α log Mdust / Mgas + cst

  • Issa et al. 1990 α = 0.85

  • Schmidt & Boller 1993 α = 0.63

  • Lisenfeld & Ferrara 1998 α = 0.52

  • Dwek 1998 (model) α = 0.77



Interpretation of SEDs

  • SED reflects:

  • Big Grains 5-250 nm (MRN, thermal)

  • Very Small Grains (nonthermal)

  • Polycyclic Aromatic Hydrocarbons (PAHs)

  • at various temperatures

  • with potentially varying size distributions



NGC 1569: ISO & SCUBA



Cold dust? Lisenfeld et al. 2002, 2005



Same observations, different views

  • Galliano et al. 2003

  • dust cold 5-7 K

  • most dust in small clumps

  • gas/dust ratio 320-680

  • (740-1600)



Evidence for dust processing

  • Spitzer: PAHs depleted in BCDGs

  • weak relation radiation field hardness

  • strong relation energy density

  • Wu et al. 2006, Rosenberg et al 2006, Higdon et al 2006

  • IRAS: PAH depletion sequence f25 / f12:

  • Im 4.5 Sm 2.9 Sc 1.8

  • Melisse & Israel 1994a, b

  • ANS-UV: behaviour 2175A bumps



H2 from FIR or submm independent from CO measurements

  • FIR or subm maps tracing dust column densities

  • Flux ratios tracing dust temperatures

  • HI maps tracing atomic gas

  • Assumption dust-to-gas ratio

  • proportional to metallicity (!)



X-factor as function of metallicity

  • Filled symbols: large beam

  • Open symbols: resolved

  • log X = -α log [O]/[H] + c

  • α = -2.3 (+/-0.3)

  • Israel 1997, 2000



Molecular gas in galaxy centers

  • (Much) less H2 than expected from CO strength

  • Yet molecular gas is >90% of the total gas mass

  • On same curve as metal-poor galaxies?



What next?

  • JCMT Legacy Survey Physical Processes in Galaxies in the Local Universe

  • 299 galaxies randomly selected from an HI-flux-limited sample, plus 32 remaining SINGS galaxies, using HARP-B and SCUBA2 (2007-2009)

  • Christine Wilson (Canada)

  • Stephen Serjeant (UK)

  • Frank Israel (NL)

  • (coordinators) and many others



JCMT LEGACY SURVEY

  • Physical properties of dust

  • Molecular gas and gas-to-dust ratios

  • Effects of galaxy morphology

  • Low-metallicity

  • Cluster environment

  • Haloes, superwinds, and AGN

  • Luminosity and dust mass functions of galaxies



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