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Recontres de Moriond XXV La Thuile, March 2005 Recontres de Moriond XXV La Thuile, March 2005 Why Starbursts? Starburst Galaxies form many stars very quickly and hence: Can give insight into the Initial Mass Function (IMF) Are very bright and can be seen at the earliest epochs helping us understand galaxy formation Are dominated by the youngest and most massive stars and many other reasons... Starburst Galaxies form many stars very quickly and hence: Can give insight into the Initial Mass Function (IMF) Are very bright and can be seen at the earliest epochs helping us understand galaxy formation Are dominated by the youngest and most massive stars and many other reasons...
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Recontres de Moriond XXV
La Thuile, March 2005
Theoretical SEDs in Starbursts:
SFRs in both the UV and IR
Brent GrovesMax Planck Institute for Astrophysics
Recontres de Moriond XXV
La Thuile, March 2005
Made By Many•Michael Dopita, Ralph Sutherland, Jörg
Fischera (RSAA,ANU)•Cristina Popescu, Richard Tuffs (MPIK)•Lisa Kewley (IfA, Hawaii) •Michiel Reuland (Leiden) •& Claus Leitherer (STSCI)
Recontres de Moriond XXV
La Thuile, March 2005
Why Starbursts?• Starburst Galaxies form many stars very
quickly and hence:• Can give insight into the Initial Mass
Function (IMF)• Are very bright and can be seen at the
earliest epochs helping us understand galaxy formation• Are dominated by the youngest and most
massive stars• and many other reasons...
Recontres de Moriond XXV
La Thuile, March 2005
Why Models?
•Understanding the Physics behind Starbursts
•Provide Pan Spectral Diagnostics to determine general parameters of Star-forming Galaxies
•Provide Self-consistent, Theoretical Star Formation Rate Measures at several Wavelengths
Recontres de Moriond XXV
La Thuile, March 2005
Star Formation Rates• Can use any part of spectrum (eg. Hα,
UV, IR)• Best is a full Spectral Energy Distribution
(SED)• But must account for dust
•∴Need to calculate dust extinction and emission
Recontres de Moriond XXV
La Thuile, March 2005
Heating Dust• As the grains absorb the incident photons
they heat up and emit thermal radiation• For large grains, the absorption and
emission reach an equilibrium state so that the grain has a steady temperature
• For small grains however things become stochastic...
Recontres de Moriond XXV
La Thuile, March 2005
Hot & Cold•Smallest grains
•have small cross-section •hence low photon
heating rate•However, small grains
also•have low specific heat•one photon causes large
increase in Temperature
Recontres de Moriond XXV
La Thuile, March 2005
Quick & Dirty Dust IR•Solve for Grain
Temperature Probability Distribution
•Convolve with Blackbody and integrate over dust sizes and types to get IR emission
•Include the emission from PAH
Recontres de Moriond XXV
La Thuile, March 2005
From Star to Finish (SED)
• Use stellar synthesis code (STARBURST99) to generate stellar spectrum of different aged bursts• Use radiative transfer code (MAPPINGS) to
determine HII spectrum and hot dust extinction and emission • Use MAPPINGS to determine PDR spectrum
of warm dust & PAH extinction and emission • Pass final spectrum through (diffuse, cold)
dusty screen
Recontres de Moriond XXV
La Thuile, March 2005
Making Stars• The Stellar Emission• Instantaneous bursts of 104 M☉ sampled at
intervals of 1 Myr up to 10 Myr• Continuous at 1 M☉
yr-1 up to 108 yrs for >10 Myr population
Recontres de Moriond XXV
La Thuile, March 2005
Blown Away•The HII Region
•All Stellar light passes through HII region
•Evaluated for 3 different Pressures: P/k=104, 106 and 107 cm-3
• Includes dynamical evolution of Stellar wind bubble
Recontres de Moriond XXV
La Thuile, March 2005
Hot & Bothered
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La Thuile, March 2005
Clearing the Mess•The Photodissociation Region
•Molecular cloud covers fraction of HII region•Absorbs Far-UV and gives warm dust and
PAH emission•Explore clearing timescale (~covering
fraction) of PDR clouds• f(t)=exp(-t/τclear)
•τclear=1, 2, 4, 8, 16 and 32 Myr
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La Thuile, March 2005
Adding PDRs
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La Thuile, March 2005
Dusty Screen•The dusty screen• Provides
attenuation by diffuse dust
•Does not include cold dust emission
Recontres de Moriond XXV
La Thuile, March 2005
Under Pressure
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Seeing through...
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A Fitting Example...
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La Thuile, March 2005
IRAS Diagnostics
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Spitzer Diagnostics
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La Thuile, March 2005
Rating Star Formation•The models then give the following
relationships between SFR and standard indicators
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Rating Star FormationStar Formation Rates for
τclear=1Myr
and for τclear=32 Myr and P/k=107 cm-3
Recontres de Moriond XXV
La Thuile, March 2005
SEDing The End• While limited, these self-consistent
theoretical starburst SEDs:• Demonstrate that two parameters control
the form of the SED• Pressure in the diffuse ISM• Molecular cloud clearing timescale
• Can reproduce observed starburst SEDs over 3 decades of frequency
Recontres de Moriond XXV
La Thuile, March 2005
Pan-SED End•These models also
•Explain the observed spread in observations on IRAS Colour-Colour Diagrams
•Predict possible diagnostics in Spitzer Diagnostic Diagrams
•Are a step forward in obtaining fully theoretical SFR indicators and explaining the links between different wavelength regimes
