research school of astronomy & astrophysics. theoretical pan-spectral energy distributions of...
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Research School of Astronomy & Astrophysics
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
Theoretical Pan-Spectral Energy Distributions of Starburst Galaxies
Mike Dopita with assistance from:Massimo Capaccioli, Joerg Fischera, Brent Groves, Lisa Kewley,
Claus Leitherer, Cristina Popescu, Maria Pereira, Ralph Sutherland & Richard Tuffs
IoA Cambridge, 7 September 2004
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
Madau Plotting for Beginners
Pick any spectral feature or portion of the galaxian SED that you can convince yourself is sensitive to SFR.
Join the outcome of such observations together in a plot of SFR per unit co-moving volume against either redshift or lookback time.
Draw conclusions on the evolution of the Universe
SFR Indicators can be lines, continuum or whatever..... remember Daniella Calzetti’s talk!
Can we reliably calibrate these theoretically in the presence of dust?
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
STIS + WFPC2 (FUV NUV I)
STIS + WFPC2 + NICMOS (NUV I H) ULIRG: MRK273
http://www.pha.jhu.edu/~meurer/research/uvlirgs.html
SFR from the UV:
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
IC 5332
SFR from H-Alpha Emission
Image from the SINGG Survey (Meurer et al. 2004)
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
but..Ionising Photons are lost by Dust Absorption
Dopita et al. 2003, ApJ, 583,
727
c.f. talk by Paul van der
Werf
HII regions
UC HII regions
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
SFR From the IR Dust Re-emission
60µm DustEmission
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
Wavelength (µm)
Dale & Helou (2002) have suggested that FIR SEDs of Starbursts may form a one-parameter
family.
Why? And what controls the one parameter?
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
To Answer these Questions, we have to consider how individual HII Regions
evolve in Starburst and Normal Galaxies.
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
Reverse ShockISM ShockContactDiscontinuity
The HII Regions Initially Evolve as Stellar Wind Blown Bubbles
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Research School of Astronomy & Astrophysics
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Initially, the expansion follows the Castor Weaver & McCray mass-loss bubble evolution.
As the bubble expands, the driving pressure decreases.
Eventually, the internal pressure becomes comparable with the pressure in the ISM, and the expansion “stalls”.
At this point, radiative losses dominate.
The time taken to reach “stall” condition, is simply proportional to the radius at stall.
The Oey and Clarke (1997) Theory
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Research School of Astronomy & Astrophysics
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....in fact, after “stalling”, the HII region
continues to expand, but in momentum-
conserving fashion.
The equation of motion:
Leads immediately to the radius-time
relation:
Momentum Conserving Shells:
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Research School of Astronomy & Astrophysics
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“Real” Evolution of a Mass-Loss Bubble
PPMLR Model (code by
Ralph Sutherland)
evolution in a log-normal
initial density distribution
cooling shown.
c.f. talk by Andrea Gilbert
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Research School of Astronomy & Astrophysics
Research School of Astronomy & Astrophysics
5.50 6.00 6.50 7.00
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
7.50
8.00
8.50
log (t / yr )5.50 6.00 6.50 7.00
19.00
19.50
20.00
20.50
21.00
log (t / yr )
P/k
104
10
10
6
8
P/k
10
10
108
6
4
The Size of an HII Region Depends on the Pressure in the ISM
...this determines the FIR SED through the Dust Temperature.... Small HII Regions
have hot dust
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Research School of Astronomy & Astrophysics
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HII Regions are smaller and brighter near the centre of a spiral galaxyi.e. in high-pressure regions (M33: data from Massey, 2002)
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Research School of Astronomy & Astrophysics
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Setting the Internal pressure to the external pressure, and assuming that the Mach Number at stall is about constant:
From which we conclude that the ionisation parameter is constant:
Stalled HII Regions have a Constant Ionization Parameter
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Research School of Astronomy & Astrophysics
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The Ionisation Parameter is Observed Constant(Kewley, Dopita & Heisler, 2000)
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At high pressures, the mean radii of HII regions are predicted to be smaller
But the derived relation:
Implies that (Conclusion #2): high-pressure HII regions should have warmer dust, Thus, warm IRAS galaxies have higher [SII] densities.
This is confirmed by observation, Kewley et al., 2001: 1E8 > P/k >1E6 c.f. our local ISM; P/k~1E4.
Dust Temperatures
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Research School of Astronomy & Astrophysics
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Use STARBURST 99 to provide intrinsic stellar SEDs.
Use MAPPINGS IIIq to compute HII region temperature and ionisation, dust absorption and dust and PAH re-emission in the mid- and far-IR. (Includes radiative transfer, grain size distribution, quantum fluctuations of the dust temperature, PAH photodissociation, and all ionized gas physics).
Ensure that any cluster of a given age is placed in its self-consistent HII region according to the derived equations, and evolve it to 10Myr in steps of 1Myr
Add the contribution of the old (10-100Myr) stars, assuming that the PAHs have been destroyed in the diffuse ISM.
Put the whole lot behind a dusty turbulent foreground screen.
SED Modelling:
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Results of SED Modelling
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Starburst SED for P/k=1E4
Older Stars
PAHs
Si Grains
[SIV][NeII][NeIII]
[SIII]
[SIII][SiII]
[OIII]
[OIII][NII]
[CI]
[CI]
Younger Stars
Starburst SED for P/k=1E4
PAHs
Si Grains[SIV]
[NeII]
[NeIII]
[SIII][SiII]
[OIII]
[OIII]
[NII]
[CI]
[CI]
Younger Stars
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5
39.0
40.0
41.0
42.0
43.0
44.0
log λ (µm)
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Starburst SED for P/k=1E7
PAHs
Si Grains[SIV]
[NeII]
[NeIII]
[SIII][SiII]
[OIII]
[OIII]
[NII]
[CI]
[CI]
Younger Stars
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5
39.0
40.0
41.0
42.0
43.0
44.0
log λ (µm)
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Research School of Astronomy & Astrophysics
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Molecular Cloud Covering Factor:Dependence on SED
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5
40.0
41.0
42.0
43.0
44.0
45.0
log λ (µm)
1 Myr
1 Myr
32 Myr
32 Myr
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Pressure Dependence of Starburst SED
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
28.0
29.0
30.0
31.0
log λ (µm)
P/k=1e7
P/k=1e6
P/k=1e4
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Computed IRAS Colour-Colour Diagrams- agree with Rush et al. (1994) Starbursts.
Some are mixed-excitation objects
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(Fishera, Dopita & Sutherland, 2003)
The Dust Attenuation Function in a Foreground Dust Screen
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All interstellar turbulence produces a log-normal distribution in density:
For isothermal non-magnetic compressible turbulence, the width of the distribution is directly related to the Mach Number of the turbulence, M:
Interstellar turbulence
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Properties of a log-normal screen
The distribution of column density is also log-normal
Thanks to large regions of low column density, Uv radiation penetrates more easily. ....The extinction curve is flatter in the UV
Dense regions are more opaque than the average in the IR ....The extinction curve is steeper in the IR, and R=Av/E(B-V) is larger than the local ISM value (~3.1)
Both of these are features of the Calzetti Law.
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The Turbulent Foreground Screen Model Fits the Calzetti Attenuation Law
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Model by Joerg Fischera
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A 3-D Representation of the Model
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Model by Joerg Fischera
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The parameters determining the SED are: 1. Pressure in the ISM and 2. The molecular cloud dissipation timescale.
High Pressure HII regions are: 1. Small, and 2. Have hot dust (i.e. warm IRAS colours).
The HII Regions in Galaxies have, on average, the same ionization parameter.
These models (Dopita et al., astro-ph) can be used to determine the global star formation rate, the ISM pressure and the molecular gas clearing timescale.
Conclusions:
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