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 COdepleted 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 concentrationsdisk, 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

Size distribution and other properties affected radiatively and dynamically active circumnuclear environment

The AGN in CENA

M83

NGC 6946, NGC 891 1

Origin of Subm/FIR emission: NGC 6822

Israel, Bontekoe & Kester, 1996 IRAS 60 microns

I

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)

Lisenfeld et al. 2002/2005

dust warm 35 K

processed dust

VSG enhanced 7-12 times

gas/dust ratio 1500-2900

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 submmindependent 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