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

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

Apr 03, 2023 138 likes •516 views

Ay 102 Physics of the Interstellar Medium supplemental material Hillenbrand Winter Term 2019-2020 The Hot Ionized Medium Xrays and UV Orion The Example of Everything Interesting! NGC 604 in M33 IRAC = dust GALEX = hot stars

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Ay 102 Physics of the Interstellar Medium

supplemental material Hillenbrand – Winter Term 2019-2020

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The Hot Ionized Medium

è Xrays and UV

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Orion – The Example of Everything Interesting!

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NGC 604 in M33

IRAC = dust GALEX = hot stars Xray = hot gas Lines = warm gas; note that bubbles visible in Hα (red) are filled with hot gas (blue) Tullmann et al (2008)

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Crab Nebula – Supernova Remnant

xray

  • ptical

near-infrared radio

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All-Sky in X-rays

(point sources removed)

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Very High-T, Very Low-n plasma

solar core this room HIM

Diffuse Galactic ISM and the IGM

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Physical Processes in the HIM

  • Because of high temperature

– have rapidly moving e- – Collisional ionization needs to be considered in addition to the excitation (described by Clu) we have discussed already. – No molecules to worry about, or neutral atoms. – Mostly far-ultraviolet and x-ray emission lines.

  • Because of low density

– Density is always lower than the critical density. – Rates (ne

2) << Rates (ne) << Rates (spontaneous de-excit.)

– As for the WIM, in the HIM, radiative decay dominates

  • collisions. So have collisions mostly from the ground level of
  • ions. This is called K-shell ionization, with n=2 called L-shell.

– Recombination line ratios are independent of density è Te.

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Diagnostics of the HIM

  • X-rays = thermal bremsstrahlung (free-free)

– T > 107 K - continuous spectrum with E-0.4 e -E/kT

  • X-ray, UV, Optical lines = high-ionization species

– 104.5 < T < 106.3 K - metals K- and L-shell ionization – 106.3 < T < 107 K - Fe L-shell collisional ionization

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Collisional Ionization Concept

  • Not enough UV to produce such high

temperatures by photo-ionization.

  • Instead, fast-moving electrons in stellar winds

and in supernova shocks è collisional ionization.

  • Steady-state ionization balance w/recombination

(as before in WIM, yet different here in HIM).

  • “Collisional Ionization Equilibrium” = C.I.E.
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Collisional Ionization Description

(sorry about the comic sans…)

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Collisional Ionization Cross Section Example

Dopita & Sutherland

Inner shells require higher energy e- and have smaller cross section

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  • A. Glassgold
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Result from the rate equations for collisional ionization in the non-LTE ISM is Saha-like curves for the different ionization states (similar in nature to those resulting from LTE photo-ionization in stars).

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Oxygen from Neutral to Highly Ionized

Temperature Determines Ionization State

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Temperature Determines Ionization State

Iron from Neutral to Highly Ionized

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Dopita & Sutherland

(WIM) (HIM)

τν =∫ ανdν

Opacity at High Energies

(13.6eV) (1keV)

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X-ray Opacity

Cross sections including H, He, metals UV photons are readily absorbed, but galaxy becomes optically thin again at E > 0.2 keV. Same as above, but cast in terms of distance.

τν = ∫ σνn dl analog expressed in energy units

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Diagnostic Lines from Ionization ++ Recombination

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X-ray Lines

Peterson & Fabian (1996)

The top panel shows helium-like and hydrogen-like charge states of various low-Z atoms. The bottom panel shows iron ions having the outer electron in the K, L, and M shell. The bottom panel indicates how the measurement of various ions in the iron series is a sensitive probe of whether plasma at a given temperature exists. Figure uses data from Arnaud & Raymond (1992).

(elemental abundance times fraction ionic abundance)

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X-ray Spectrum

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IR opt UV x-ray IR opt UV x-ray

These hot lines sit on top of a continuum spectrum which comes from “free-free” emission

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Free-Free Continuum a.k.a. Bremsstrahlung Radiation

https://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/xrays.htm

Range of relative KE between the free e- and the heavy ion+ è ”continuum” process

E-0.4 e -E/kT

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  • J. Williams

Same process occurs at low energies (radio) for p and e in the WIM

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The Emission Measure

  • D. Dallacasa
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CGM / IGM

  • CGM refers to the gas and dark matter outside of

galaxies, but still within the radius of the collapsed, virialized cosmological dark matter structure around the galaxies. This is the interface zone between galactic inflows and outflows.

  • IGM refers to the even lower density gas, located
  • utside of these radii, which also displays structure.
  • Most of the baryons appear to be in the CGM!

So far, the extremely diffuse, hot ionized gas is our

  • nly probe.
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  • T. Greve
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Tumlinson et al 2017; ARAA

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Spectrum of background QSO absorbed by CGM of foreground QSO

Background QSO spectrum Foreground QSO spectrum 𝑆"

Flux Flux

slide courtesy P. Parihar

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Tumlinson et al 2017; ARAA

CGM gas at 3x105 - 107 K !

UV Absorption Lines

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X-ray Halos in Galaxy Clusters

Abell 2029

IGM gas at 107-108 K !

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