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 – G : A Case Study and Galactic Plane Surveys

Star Formation in our Galaxy Introduction to Star Formation Throughout the Galaxy 1.Why study star formation? 2.The Galactic ecology 3.Dark clouds, complexes and giant molecular clouds 4.The Milky Way at different wavelengths 5.Young stellar object classes 6.Disks, jets and outflows 7.Gravitational collapse 8.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

The Galactic Ecology Supernova Molecular Cloud Cores Young stellar objects Stars High mass Low mass Planetary nebula White dwarf Neutron star Black hole Triggering SN shocks HMS winds Outflows

Cores, Dark clouds, Complexes and Giant Molecular Clouds Giant Molecular Clouds: ~10 5 solar masses ~50pc

Cores, Dark clouds, Complexes and Giant Molecular Clouds Dark Cloud Complexes: ~10 4 solar masses ~10pc

Cores, Dark clouds, Complexes and Giant Molecular Clouds

NH 3 (1,1) Dark Clouds

Optical Near-Infrared Masses: Between fractions and a few x 10 solar masses Sizes: ~1pc

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 1.2 mm Dust Continuum C 18 O N 2 H + Optical Near-Infrared Masses: Between fractions and a few x 10 solar masses Sizes: ~1pc

Properties of Cores, Dark clouds, Complexes and Giant Molecular Clouds Type n Size T Mass [cm -3 ] [pc] [K] [M sun ] Giant Molecular Cloud Dark Cloud Complex 5x Individual Dark Cloud Dense low-mass cores Dense high-mass cores >

Planck's Black Body

Wien's Law max = 2.9/T [mm] Examples: The Sun T  6000 K  max = 480 nm (optical) Humans T  310 K  max = 9.4  m (MIR) Molecular Clouds T  20 K  max = 145  m (FIR) Cosmic Background 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 - 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 Bachiller et al Snell et al. 1980

The prototypical molecular outflow HH211

General outflow properties - Jet velocities km/s Outflow velocities km/s - Estimated dynamical ages between 10 3 and 10 5 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

Snell et al Spectral Line Profiles Outflow wings Infall

1.Rising T ex along line of sight 2.Velocity gradient 3.Line optically thick 4.An additional optically thin line peaks at center Spectral Line Profiles Outflow wings Infall

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

Most stars are formed in clusters (Maybe) ALL High Mass Stars Formed in Clusters

Spitzer 3-colour image of NGC Courtesy Rob Gutermuth (CfA)

Clustered Star Formation Walsh et al Red & Blue = HCO + (1-0) Greyscale = N 2 H + (1-0) + = dust continuum cores

Clustered Star Formation