Madau Plotting for Beginners

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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





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?





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:





IC 5332

SFR from H-Alpha Emission

Image from the SINGG Survey (Meurer et al. 2004)





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





SFR From the IR Dust Re-emission

60µm DustEmission





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?





To Answer these Questions, we have to consider how individual HII Regions

evolve in Starburst and Normal Galaxies.





Reverse ShockISM ShockContactDiscontinuity

The HII Regions Initially Evolve as Stellar Wind Blown Bubbles





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





....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:





“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





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





HII Regions are smaller and brighter near the centre of a spiral galaxyi.e. in high-pressure regions (M33: data from Massey, 2002)





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





The Ionisation Parameter is Observed Constant(Kewley, Dopita & Heisler, 2000)





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





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:





Results of SED Modelling





Starburst SED for P/k=1E4

Older Stars

PAHs

Si Grains

[SIV][NeII][NeIII]

[SIII]

[SIII][SiII]

[OIII]

[OIII][NII]

[CI]

[CI]

Younger Stars


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)






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)





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





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





Computed IRAS Colour-Colour Diagrams- agree with Rush et al. (1994) Starbursts.

Some are mixed-excitation objects





(Fishera, Dopita & Sutherland, 2003)

The Dust Attenuation Function in a Foreground Dust Screen





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





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.





The Turbulent Foreground Screen Model Fits the Calzetti Attenuation Law





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Model by Joerg Fischera





A 3-D Representation of the Model

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Model by Joerg Fischera













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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Madau Plotting for Beginners