Theoretical SEDs in Starbursts SFRs in both the
Theoretical SEDs in Starbursts: SFRs in both the UV and IR Brent Groves Max 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 (If. A, 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 dominated by the youngest and most massive stars • and many other reasons. . . Are very bright and can be seen at the earliest epochs helping us understand galaxy formation 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 (STARBURST 99) 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 Recontres de Moriond XXV La Thuile, March 2005
Clearing the Mess • The Photodissociation Region • • Molecular cloud covers fraction of HII region • Explore clearing timescale (~covering fraction) of PDR clouds • • f(t)=exp(-t/τclear) Absorbs Far-UV and gives warm dust and PAH emission τclear=1, 2, 4, 8, 16 and 32 Myr Recontres de Moriond XXV La Thuile, March 2005
Adding PDRs Recontres de Moriond XXV 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 Recontres de Moriond XXV La Thuile, March 2005
Seeing through. . . Recontres de Moriond XXV La Thuile, March 2005
A Fitting Example. . . Recontres de Moriond XXV La Thuile, March 2005
IRAS Diagnostics Recontres de Moriond XXV La Thuile, March 2005
Spitzer Diagnostics Recontres de Moriond XXV La Thuile, March 2005
Rating Star Formation • The models then give the following relationships between SFR and standard indicators Recontres de Moriond XXV La Thuile, March 2005
Rating Star Formation Rates for τclear=1 Myr 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 Recontres de Moriond XXV La Thuile, March 2005
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