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 FormationThroughout the Galaxy

1.Why study star formation?2.The Galactic ecology3.Dark clouds, complexes and giant molecular clouds4.The Milky Way at different wavelengths5.Young stellar object classes6.Disks, jets and outflows7.Gravitational collapse8.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

TriggeringSN shocks

HMS w

inds

Outflow

s

Cores, Dark clouds, Complexes andGiant Molecular Clouds

Giant Molecular Clouds:~105 solar masses~50pc

Cores, Dark clouds, Complexes andGiant Molecular Clouds

Dark Cloud Complexes:~104 solar masses~10pc

Cores, Dark clouds, Complexes andGiant Molecular Clouds

NH3 (1,1)

Dark Clouds

Dark CloudsOptical Near-InfraredMasses:

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 C18O N2H+

Optical Near-InfraredMasses:Between fractions and a few x 10 solar masses

Sizes:~1pc

Properties of Cores, Dark clouds, Complexes and Giant Molecular

CloudsType n Size T Mass [cm-3] [pc] [K] [Msun]

Giant Molecular Cloud 102 50 15 105

Dark Cloud Complex 5x102 10 10 104

Individual Dark Cloud 103 2 10 30

Dense low-mass cores 104 0.1 10 10

Dense high-mass cores >105 0.1-1 10-30 100-1000

Planck's Black Body

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 outflowsHerbig 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. 1990Snell et al. 1980

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

Snell et al. 1980

Spectral Line Profiles• Outflow wings

• Infall

1. Rising Tex along line of sight2. Velocity gradient3. Line optically thick4. An additional optically thin line peaks at center

Spectral Line Profiles• Outflow wings

• Infall

Infall ProfilesHCO+ (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 StarsFormed 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)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

Walsh et al. 2007

Red & Blue = HCO+ (1-0)

Greyscale = N2H+ (1-0)

+ = dust continuum cores

Clustered Star Formation