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Star Formation in our Galaxy Dr Andrew Walsh (James Cook University, Australia) Lecture 1 – Introduction to Star Formation Throughout the Galaxy Lecture 2 – Chemistry and Star Formation Lecture 3 – High Mass Star Formation and Masers Lecture 4 – G305.2+0.2: A Case Study and Galactic Plane Surveys Star Formation in our Galaxy Introduction to Star Formation Throughout the Galaxy 1. 2. 3. 4. 5. 6. 7. 8. Why study star formation? The Galactic ecology Dark clouds, complexes and giant molecular clouds The Milky Way at different wavelengths Young stellar object classes Disks, jets and outflows Gravitational collapse Clustered star formation Why Study Star Formation? Star formation is the process that determines the properties of the major building blocks of the universe: Stars, Planets and Galaxies Why Study Star Formation? The birth of stars is the most poorly understood stage of evolution of stars Star formation is one of the most beautiful processes in the cosmos! McCaughrean et al. 1996 Neutron star The Galactic Ecology Molecular Cloud Supernova Cores Black hole High mass Young stellar objects White dwarf Stars Planetary nebula Low mass Cores, Dark clouds, Complexes and Giant Molecular Clouds Giant Molecular Clouds: ~105 solar masses ~50pc Cores, Dark clouds, Complexes and Giant Molecular Clouds Dark Cloud Complexes: ~104 solar masses ~10pc Cores, Dark clouds, Complexes and Giant Molecular Clouds NH3 (1,1) Dark Clouds Dark Clouds Masses: Between fractions and a few x 10 solar masses Sizes: ~1pc Optical Near-Infrared Interstellar Extinction Red light is absorbed by dust less than blue light We can see deeper into dust-enshrouded objects at longer wavelengths. Extinction ~ λ-1.7 Dark Clouds Masses: Between fractions and a few x 10 solar masses Optical Near-Infrared Sizes: ~1pc 1.2 mm Dust Continuum C18O N2H+ Properties of Cores, Dark clouds, Complexes and Giant Molecular Clouds Type Giant Molecular Cloud n Size [cm-3] [pc] T [K] Mass [Msun] 102 50 15 105 5x102 10 10 104 Individual Dark Cloud 103 2 10 30 Dense low-mass cores 104 0.1 10 10 10-30 100-1000 Dark Cloud Complex Dense high-mass cores >105 0.1-1 Planck's Black Body Planck's Black Body Wien's Law max = 2.9/T [mm] Examples: The Sun Humans Molecular Clouds Cosmic Background T 6000 K max= 480 nm (optical) T 310 K max= 9.4 mm (MIR) T 20 K max= 145 mm (FIR) T 2.7 K max= 1.1 mm (mm) Spectral Energy Distribution Class 0, I, II and III Young Stellar Objects McCaughrean et al. 1996 Discovery of outflows Herbig 1950, 1951; Haro 1952, 1953 Initially thought to be embedded protostars but soon spectra were recognized as caused by shock waves --> jets and outflows Discovery of outflows Bachiller et al. 1990 Snell et al. 1980 - In the mid to late 70th, first CO non-Gaussian line wing emission detected (Kwan & Scovile 1976). - Bipolar structures, extremely energetic, often associated with HH objects The prototypical molecular outflow HH211 General outflow properties - Jet velocities 100-500 km/s <==> Outflow velocities 10-50 km/s Estimated dynamical ages between 103 and 105 years Size between 0.1 and 1 pc Force provided by stellar radiation too low (middle panel) --> non-radiative processes necessary! Mass vs. L Force vs. L Outflow rate vs. L Wu et al. 2004, 2005 Spectral Line Profiles • Outflow wings • Infall Snell et al. 1980 Spectral Line Profiles • Outflow wings • Infall 1. 2. 3. 4. Rising Tex along line of sight Velocity gradient Line optically thick An additional optically thin line peaks at center Infall Profiles HCO+ (1-0) Optically thick N2H+ (1-0) Optically thin Walsh et al. 2006 Infall Profiles Walsh et al. 2006 Clustered Star Formation Clustered Star Formation Most stars are formed in clusters (Maybe) ALL High Mass Stars Formed in Clusters Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA) Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA) Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA) Clustered Star Formation Red & Blue = HCO+ (1-0) Greyscale = N2H+ (1-0) + = dust continuum cores Walsh et al. 2007 Clustered Star Formation
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