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Madau Plotting for Beginners

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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Madau Plotting for Beginners

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  1. Theoretical Pan-Spectral Energy Distributions of Starburst GalaxiesMike Dopita with assistance from:Massimo Capaccioli, Joerg Fischera, Brent Groves, Lisa Kewley, Claus Leitherer, Cristina Popescu, Maria Pereira, Ralph Sutherland & Richard TuffsIoA Cambridge, 7 September 2004

  2. 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?

  3. SFR from the UV: STIS + WFPC2 (FUVNUVI) STIS + WFPC2 + NICMOS (NUVIH) ULIRG: MRK273 http://www.pha.jhu.edu/~meurer/research/uvlirgs.html

  4. SFR from H-Alpha Emission IC 5332 Image from the SINGG Survey (Meurer et al. 2004)

  5. but..Ionising Photons are lost by Dust Absorption UC HII regions c.f. talk by Paul van der Werf HII regions Dopita et al. 2003, ApJ, 583, 727

  6. SFR From the IR Dust Re-emission 60µm Dust Emission

  7. Dale & Helou (2002) have suggested that FIR SEDs of Starbursts may form a one-parameter family.Why? And what controls the one parameter? Wavelength (µm)

  8. To Answer these Questions, we have to consider how individual HII Regions evolve in Starburst and Normal Galaxies.

  9. The HII Regions Initially Evolve as Stellar Wind Blown Bubbles

  10. The Oey and Clarke (1997) Theory • 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.

  11. Momentum Conserving Shells: • ....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:

  12. “Real” Evolution of a Mass-Loss Bubble evolution in a log-normal initial density distribution cooling shown. PPMLR Model (code by Ralph Sutherland) c.f. talk by Andrea Gilbert

  13. The Size of an HII Region Depends on the Pressure in the ISM P/k 8 10 4 10 6 10 6 10 4 10 8 10 P/k ...this determines the FIR SED through the Dust Temperature.... Small HII Regions have hot dust

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

  15. Stalled HII Regions have a Constant Ionization Parameter • 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:

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

  17. Dust Temperatures • 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.

  18. SED Modelling: • 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.

  19. Results of SED Modelling

  20. Starburst SED for P/k=1E4 Starburst SED for P/k=1E4 Si Grains [SIII] [OIII] [SIII] [OIII] Younger Stars Younger Stars PAHs [SiII] [SiII] [NII] [NeII] [NII] PAHs [NeII] [OIII] [OIII] [NeIII] [SIV] [NeIII] [SIV] Si Grains [SIII] [CI] [CI] [CI] [CI] Older Stars

  21. Starburst SED for P/k=1E7 [OIII] [SIII] Younger Stars [SiII] [NII] [NeII] PAHs [OIII] [NeIII] [SIV] Si Grains [CI] [CI]

  22. Molecular Cloud Covering Factor: Dependence on SED 1 Myr 32 Myr 32 Myr 1 Myr

  23. Pressure Dependence of Starburst SED P/k=1e7 P/k=1e6 P/k=1e4

  24. Computed IRAS Colour-Colour Diagrams - agree with Rush et al. (1994) Starbursts. Some are mixed-excitation objects

  25. (Fishera, Dopita & Sutherland, 2003)

  26. Interstellar turbulence • 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:

  27. 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.

  28. The Turbulent Foreground Screen Model Fits the Calzetti Attenuation Law

  29. Model by Joerg Fischera

  30. A 3-D Representation of the Model Model by Joerg Fischera

  31. Conclusions: • 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.

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