Ay 102 Physics of the Interstellar Medium supplemental material - - PowerPoint PPT Presentation

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ay 102 physics of the interstellar medium
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Ay 102 Physics of the Interstellar Medium supplemental material - - PowerPoint PPT Presentation

Jun 15, 2023 219 likes •592 views

Ay 102 Physics of the Interstellar Medium supplemental material Hillenbrand Winter Term 2019-2020 Radiative Transfer The interaction of photons and matter! whfreeman.com Important variables: energy of the photons (

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SLIDE 1

Ay 102 Physics of the Interstellar Medium

supplemental material Hillenbrand – Winter Term 2019-2020

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SLIDE 2

Radiative Transfer

  • The interaction of photons and matter!
  • Important variables:
  • energy of the photons (è frequency)
  • temperature and density of the gas (è cross section)
  • presence and size of dust (è cross section)

whfreeman.com

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SLIDE 3
  • D. Fischer

n1, σ1 n2, σ2 n, σ

Can also have an emission component, which contributes photons instead of removing them è d Iν = jν ρds

Iλ

recall that n σ = k ρ

Iλ

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SLIDE 4

Equation of Radiative Transfer

In analyzing spectra need to consider both continuum and line processes. Optical depth τν (with dτν = κν ρ ds) accounts for interaction between matter and the radiation field.

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SLIDE 5

Illustration (courtesy of K. Dullemond)

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SLIDE 6
  • Rad. trans. through a cloud of fixed T

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν < Iν

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SLIDE 7

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν < Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 8

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν < Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 9

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν < Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 10

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν > Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 11

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν > Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 12

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν > Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 13

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Sν > Iν

  • Rad. trans. through a cloud of fixed T
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SLIDE 14
  • D. Fischer

Many Ways to Remove Photons = Opacity

(continuum opacity) (line opacity) (continuum opacity)

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SLIDE 15
  • D. Fischer

Many Ways to Remove Photons = Opacity

(continuum opacity) (continuum opacity)

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SLIDE 16

Opacity is mostly from dust at UV through infrared and millimeter Opacity is entirely from gas below the lyman limit

Resulting Total Absorption Cross Section

Showing wavelength dependence of the continuum only. There can also be superposed line opacity.

10 µm 1 µm 0.1 µm

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SLIDE 17
  • T. Montmerle
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SLIDE 18

Far

  • UV

Extreme-UV Soft x-ray Hard x-ray Ercolano & Pascucci

It Doesn’t Take Much Column to Get Rid of UV

12.4 nm à Av = 1 mag This is a hot emission region seen through increasing amounts

  • f cooler gas.

(showing continuum and lines)

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SLIDE 19

Radiative Transfer and Spectral Lines

  • Concerning line opacity, we are going to spend some

time understanding energy levels and the “transitions” between them for:

  • Atoms / Ions (Grotrian diagrams for electronic levels)
  • Molecules (Jablonski diagrams for rotational and vibrational)
  • The balance of the upward and downward transitions --

combined with the 1/ 4π directional probability for photon emission −− is a source of opacity.

  • Then the solutions to the Radiative Transfer Equation

determine what we actually observe.

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SLIDE 20

Line Profiles and Strengths

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SLIDE 21

Emission vs. absorption lines

Hot foreground layer Flux l Cool foreground layer Flux l

  • K. Dullemond
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SLIDE 22
  • J. Williams

how strong is the line?

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SLIDE 23

Thermal Line Width

Profile strength Fν ν σ νline

  • K. Dullemond
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SLIDE 24

Illustration (courtesy of K. Dullemond)

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SLIDE 25

Emission vs. absorption lines

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

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SLIDE 26

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Emission vs. absorption lines

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SLIDE 27

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Emission vs. absorption lines

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SLIDE 28

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

line is “saturated”

Emission vs. absorption lines

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SLIDE 29

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Emission vs. absorption lines

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SLIDE 30

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Emission vs. absorption lines

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SLIDE 31

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

Emission vs. absorption lines

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SLIDE 32

Iν,bg Iν,out T

cloud

τcloud

Tbg=6000 K

line is “saturated”

Emission vs. absorption lines

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SLIDE 33

IGM example

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SLIDE 34

Lyman Series Absorption è NHI

Flux Velocity

line is “saturated” higher level lines from same species are weaker

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SLIDE 35
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SLIDE 36
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SLIDE 37