Transcript DUST IN DWARF GALAXIES - Osservatorio Astrofisico di Arcetri

DUST AND MOLECULES IN
SPIRAL GALAXIES
as seen with the JCMT
F.P. Israel, Sterrewacht Leiden
ATOMS and MOLECULES ...
... AND DUST
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SCUBA 850 mu
M51 Line and Continuum
M51 J=3-2 CO
depleted in center, enhanced in arms
ISM in Spiral Galaxies
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Atomic gas avoids center
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Molecular gas often concentrated in center
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Dust emission follows total gas
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Metallicity & excitation gradients
Center: exclusively molecular
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Inner disk: molecules dominant
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Outer disk: atoms dominant
Nuclear CO concentrations
disk, torus or spiral?
12CO degeneracy
resolved by 13co
Molecules in galaxy centers
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Concentrated within R = 0.5 kpc
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High contrast with disk CO
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CO pollutes broadband continuum!
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Physical parameters only from several line
transitions!
At least two components:
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Lukewarm and dense
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Hot and tenuous
Hot and tenuous gas >50% of mass
Dust in galaxy centers
Size distribution and other properties affected
radiatively and dynamically active
circumnuclear environment
heating/cooling depends on:
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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
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
α = 0.77
(model)
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
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weak relation radiation field hardness
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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
Melisse & Israel 1994a, b
ANS-UV: behaviour 2175A bumps
Sc
1.8
H2 from FIR or submm
independent from CO measurements
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FIR or subm maps tracing dust column densities
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Flux ratios tracing dust temperatures
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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
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(Much) less H2 than expected from CO
strength
Yet molecular gas is >90% of the total gas
mass
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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-fluxlimited sample, plus 32 remaining SINGS
galaxies, using HARP-B and SCUBA2 (20072009)
Christine Wilson (Canada)
Stephen Serjeant (UK)
Frank Israel (NL)
(coordinators) and many others
JCMT LEGACY SURVEY
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Physical properties of dust
Molecular gas and gas-to-dust ratios
Effects of galaxy morphology
 Low-metallicity
 Cluster environment
 Haloes, superwinds, and AGN
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Luminosity and dust mass functions of
galaxies