3.2 Dust in the ISM Flashcards

1
Q

How does dust interact with radiation?

A

It effectively reprocesses it

It can scatter, absorb and emit it

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2
Q

What is dust made up of?

A

Mainly small (0.1-1)μm grains of Si, C, O

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3
Q

What are the two sources of dust origin?

A

Stellar winds and supernova remnants

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4
Q

Describe the origin of dust from stellar winds

A

Very young stars/evolved stars (not MS) can expel the metal rich outer layers of their atmosphere

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5
Q

Describe the origin of dust from supernova remnants

A

Metal rich material cooling down after explosions

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6
Q

What percent of mass and light does dust contribute in the MW?

A

It is 0.1% of the mass, but reprocesses 30% of the light

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7
Q

Define extinction

A

The change in magnitude between the magnitude measured in the presence of dust and the magnitude measured without the presence of dust

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8
Q

How does distance affect distance indicators?

A

It increases the apparent magnitude which increases the DM

- Objects appear further away

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9
Q

What are the three regimes of scattering and its wavelength dependence?

A
Small grains (r << λ)
Intermediate grains ( r ~ λ)
Big grains (r > λ)
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10
Q

Describe what happens in the small grain regime of scattering (r &laquo_space;λ)
r - radius of dust

A

Called Rayleigh scattering
- Causes bluer photons to scatter more effectively than redder photons
σ ~ λ^-4

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11
Q

Describe what happens in the intermediate grain regime of scattering (r ~ λ)

A

Mie scattering σ ~ λ^-1

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12
Q

Describe what happens in the big grain regime of scattering (r&raquo_space; λ)

A

No dependence on wavelength anymore, σ is constant

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13
Q

What is fragmentation, and what is a consequence of it?

A

Dust grains can collide and fragment, so small grains always out number big grains so Rayleigh scattering is important
Observe in IR

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14
Q

How can we measure relative extinction?

A

Measure extinction at two different wavelengths and call it reddening
reddening = E(B-V) = A_B - A_V
where B and V are the blue and visible bands

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15
Q

What relationship does the extinction law provide?

A

A relation linking reddening to a parameter called K_λ

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16
Q

Describe the graph of K_λ against λ for our MW and for LMCs

A

Steep at short λ due to Rayleigh scattering (and small grains)
K_λ is prop. to λ^-1 for most the range (Mie scattering)
Bump at 220nm due to graphite (C crystals)

17
Q

What is the wavelength dependence of extinction laws driven by?

A

Formation mechanisms for dust (size) and metallicity of host galaxy

18
Q

What does the Calzetti law describe?

A

Galaxies with intense star formation (star burst galaxies)